After Thomas stopped Jonathan Toews, Seguin scored on a forehand move on Boston's first shot. Thomas then denied Patrick Kane on a forehand bid. After Patrice Bergeron lost control of the puck on his attempt to close out the win, Thomas stuffed Patrick Sharp to complete the victory.
The Bruins improve to 2-3-0 on the season with a strong all-around effort in Chicago and head home to face the Carolina Hurricanes at the Garden on Tuesday.
End Overtime, 2-2: The Bruins carried the play for most of the extra session, then survive a late push by Chicago and this one will go to a shootout.
Overtime, 2:26, 2-2: Rich Peverley had two golden chances to end it, but he's denied with a shot from the right slot, then has a clean breakaway but sends his backhander wide of the net.
Overtime, 0:00, 2-2: The extra session is under way in Chicago, with five minutes of sudden death 4-on-4 action followed by a shootout if necessary.
End Regulation, 2-2: Sixty minutes won't be enough to settle this one. The Bruins have earned at least one point, and will go for the second one as this one heads to overtime.
Third Period, 19:33, 2-2: The Bruins again come up empty on the power play, but Dennis Seidenberg nearly ended that drought and gave Boston the lead as he clanged a blast off the post.
Third Period, 17:33, 2-2: The Blackhawks even it up as Patrick Sharp is called for holding Boychuk's stick. It will be 4 on 4, then the Bruins will get a brief late power play.
Third Period, 16:25, 2-2: The Bruins face a huge penalty kill here as Benoit Pouliot gets reckless with his stick and clocks Brent Seabrook on the back of the head to draw a two-minute minor for high-sticking.
Third Period, 15:57, 2-2: The Bruins threaten again as Seguin dances through the defense and fires in a shot from the right side that forces Crawford to flash out a pad.
Third Period, 12:58, 2-2: The Bruins continue to press for the go-ahead goal, with a strong shift from Seguin and Co. on the top line nearly getting that elusive tally.
Third Period, 7:56, 2-2: The Bruins pull even on a great play by Johnny Boychuk, who sets up Nathan Horton for his first goal of the year.
Boychuk passed the puck to himself off the boards and went all the way down below the goal line in the Chicago end, then passes out to Horton in the left circle for the shot. Seguin picks up the secondary assist.
Third Period, 7:16, Blackhawks 2-1: The Bruins shake up the lines a bit to have an extra faceoff guy on the ice, and the combo of Bergeron, Lucic and Seguin create some havoc in front and nearly tie this one up.
Third Period, 6:42, Blackhawks 2-1: The pace has slowed a bit here in the third, with both teams charged with icing calls as the back and forth action of the first two periods has been clogged up by a more defensive approach to the final frame.
Third Period, 2:09, Blackhawks 2-1: The Bruins kill off that penalty thanks to a big save early by Thomas. Brad Marchand and Daniel Paille created a shorthanded chance late, then Marchand started a scrum with a slight bump on Crawford.
Third Period, 0:09, Blackhawks 2-1: The Bruins will have an early penalty to kill in the third as Bergeron is called for boarding Michael Frolik just nine seconds into the period.
Third Period, 0:00, Blackhawks 2-1: The final frame is under way in Chicago, with the Bruins in need of a rally to avoid falling to 1-4-0 to start the season.
Second Intermission Notes: The Bruins put together a better second period and got on the board with Chris Kelly's shorthanded tally, but the Blackhawks answered right back and take a 2-1 lead into the third.
The Bruins put more pressure on Corey Crawford, outshooting Chicago 10-7 in the second and 23-20 overall. They're also outhitting the Hawks 28-25. Even Nathan Horton got into the act, getting his first hit of the season at 8:48 of the second.
Patrice Bergeron also had three hits and is 10-3 on draws. As usual, he's doing all the little things right, with a steal from behind on Nick Leddy setting up Milan Lucic for a scoring chance.
End Second Period, Blackhawks 2-1: The first 40 minutes are in the books, and after an exchange of goals in the second the Blackhawks will take a one-goal lead into the third.
Second Period, 16:29, Blackhawks 2-1: Another unsuccessful power play for the Bruins, as Frolik is out of the box and the sides back at even strength.
Second Period, 14:29, Blackhawks 2-1: Dangerous hit from behind sends Michael Frolik to the box for boarding and Chris Kelly to the bench. Kelly appears to be OK, and the Bruins will try to finally end their power-play drought.
Second Period, 11:00, Blackhawks 2-1: Patrick Sharp almost gets one past Thomas with a shot from the right side, but Thomas gets enough of a piece to deflect it up and over the net.
Second Period, 9:28, Blackhawks 2-1: Good up and down action with both teams creating chances, but Thomas and Crawford have been up to the task in this last stretch to keep the score down.
Second Period, 5:32, Blackhawks 2-1: Chris Kelly almost really has a night as he beats Crawford clean with a long wrister but clangs it off the post in a bid to tie this game again.
Second Period, 2:51, Blackhawks 2-1: The Blackhawks answer right back as Patrick Kane scores from the left circle to put Chicago back on top.
Second Period, 1:33, 1-1: The Bruins pull even with a shorthanded tally as Chris Kelly scores from Rich Peverley.
Peverley led a 2 on 1, carrying the puck down the right wing and crossing it to kelly at the left post for the goal.
Second Period, 0:24, Blackhawks 1-0: The Blackhawks get their first power play of the night as Nathan Horton is sent to the box for goalie interference.
Second Period, 0:00, Blackhawks 1-0: The middle frame is under way in the Chicago, with the Bruins looking to pull even in this battle of the last two Cup champs.
First Intermission Notes: The Bruins showed some life and a better physical game in the first, but still came away from the opening period down 1-0.
Boston had 16 hits in the first after managing just 12 in the entire game in Carolina. Gregory Campbell also dropped the gloves for the team's first fight of the year.
The Bruins still couldn't score on the power play though, failing to convert the game's only chance so far. Boston is now 1 for 17 on the year, failing to cash in on 16 straight opportunities after scoring on their first power play of the year.
The shot count is even at 13-13, but Tim Thomas has had to come up with the tougher saves. he's done his job to keep the Bruins in the game, with the lone goal coming off a bad Andrew Ference turnover that gave Bryan Bickell a clean breakaway.
End First Period, Blackhawks 1-0: The opening 20 minutes are in the books, with Chicago taking a one-goal lead into intermission.
It could have been worse, but Tim Thomas came up with some big saves, including one on Dan Carcillo just after Bryan Bickell's goal.
One positive: Johnny Boychuk did return to the ice after being shaken up earlier in the period when he was hit into the boards, then blocked a shot.
First Period, 16:21, Blackhawks 1-0: The Blackhawks strike first as Bryan Bickell steals an Andrew Ference crossing pass at center ice and breaks in alone ahead of the defense.
Bickell beats Thomas with a forehand and Chicago has the one-goal lead.
First Period, 14:24, 0-0: Thomas denied Kane again, this time when the Blackhawks center takes a long outlet pass, pulls off a spin move to shed a defender and fires a backhander from in front. But Thomas smothers that shot for a whistle.
First Period, 11:17, 0-0: The Bruins fail to convert another power play, though they did look a little better on that man advantage and created some chances.
First Period, 9:17, 0-0: The Bruins get the first power play of night with Stalberg sent off for tripping. They ended the fight drought, can they end the power-play drought?
First Period, 7:48, 0-0: The gloves are finally off, with Gregory Campbell and Jamal Mayers squaring off immediately after taking a draw against each other.
It was a long battle, but not too much was landed as they went into spin mode with Campbell eventually scoring the takedown.
First Period, 6:38, 0-0: Tough shift for Johnny Boychuk, who was jammed hard into boards by Dan Carcillo, then blocked a Duncan Keith shot. Boychuk heads off ice in obvious pain appearing to hold his right arm.
First Period, 4:05, 0-0: Thomas with another big early save, flashing the glove to snag Kane's backhander as Kane drove right to the net on a give-and-go with Stalberg.
First Period, 4:05, 0-0: Thomas has been tested early and has come up with big saves on both of Chicago's young stars, stopping Patrick Kane on a drive from the left side despite a screen in front, then blocking a blistering one-timer by Jonathan Toews.
First Period, 1:12, 0-0: Milan Lucic has the first good scoring chance of the game with a bid from the right slot off a feed from Tyler Seguin, but Lucic can't put it home.
First Period, 0:00, 0-0: This one is under way in Chicago, with the Bruins going with the Marchand-Bergeron-Peverley line to start, along with Seidenberg and Corvo on defense and Thomas in goal.
Chicago counters with Bryan Bickell, Dave Bolland and Michael Frolik up front, Niklas Hjalmarsson and Brent Seabrook on the blue line and Corey Crawford in net.
8:30 p.m.: Late lineup change for the Hawks, who will have John Scott in the lineup. Rostislav Olesz will sit out instead. So maybe the Bruins will get their first fight of the season in this one after all.
8:20 p.m.: The scratches have been announced. No surprises on the Boston side with Krejci and McQuaid both out with injuries.
Chicago has scratched Marian Hossa, who cannot go with the upper-body injury that forced him to miss the morning skate, Sami Lepisto and John Scott. Apparently the Blackhawks aren't too worried about Shawn Thornton exacting any revenge for the chirps from the Chicago bench when he was cut in the face by a skate in last year's meeting. Scott is Chicago's 6-foot-8, 258-pound enforcer, but he won't be able to enforce anything from the press box.
Viktor Stalberg does return from a knee injury and will play his first game of the year for Chicago.
8:15 p.m.: No changes to the Bruins lines in warm-ups, with Bartkowski sliding into McQuaid's spot next to Andrew Ference on the third defense pairing.
Here's how they should line up in this one:
8 p.m.: Tim Thomas and Corey Crawford did lead the teams onto the ice for warm-ups, so that will be the goalie matchup in this one as expected.
7:30 p.m.: The last two Stanley Cup winners will clash in just about an hour in Chicago as the 2010 champs Blackhawks host the reigning champion Bruins.
Tim Thomas is expected to be in goal for Boston, with Chicago countering with Corey Crawford.
The Bruins will be without center David Krejci (core injury) and defenseman Adam McQuaid (head/neck). Tyler Seguin will remain in Krejci's spot centering the top line, while Matt Bartkowski fills in for McQuaid on the blue line.
The Blackhawks could be without Marian Hossa, who did not participate in the morning skate. he has an upper-body injury and will be a game-time decision.
8 a.m. ET: The Bruins' title defense hasn't gotten off to the start they hoped for with three losses in their first four games, but on Saturday Boston will get a chance to put things back on track against a team that knows exactly what the Bruins are dealing with in trying to overcome the Stanley Cup hangover.
The Blackhawks struggled mightily out of the gate last year after winning the Cup in 2010. They barely snuck into the playoffs as the eighth seed in the West, then lost in the opening round. The Bruins don't want to suffer the same fate, so they know they can't dig themselves too big a hole in the early going of the season.
This year's Chicago squad, well rested after its early postseason exit, isn't having many early problems. The Blackhawks are 2-1-0, winning two straight at home over Dallas and Winnipeg. Patrick Kane has been moved from first-line wing to center on the second line, and has responded with 1-4-5 totals in three games.
That move has given the Blackhawks better balance offensively, and will make them an even tougher opponent. But that might be exactly what the Bruins need after back-to-back losses to Colorado and Carolina, two teams that failed to make the playoffs last season.
"It's certainly a good team," Bruins coach Claude Julien said of Chicago. "We respect that and we know what they went through last year. Every team is ready for us and I don't think anybody is going to feel sorry for us right now. It's up to us to battle our way through. Sometimes a real tough opponent is what you need to get the best out of a lot of us, so hopefully that's the case and we come out and play a little bit more like our team and make sure we get those good habits back that make us successful."
The Bruins will be without center David Krejci, who remains back in Boston with a core injury, and defenseman Adam McQuaid, who was injured Wednesday in Carolina when he fell headfirst into the boards. Chicago, meanwhile, has a pair of players with New England college ties close to returning.
Boston College product Ben Smith (concussion) won't play Saturday but has begun practicing again, while Viktor Stalberg (knee), who played at Vermont, could return to the lineup in this game.
There's also the potential for some rough stuff. The Bruins haven't had a fight yet this season, but that could change if Shawn Thornton still harbors a grudge from when the Chicago bench chirped him going off the ice with a cut from a skate that required over 40 stitches in the clubs' last meeting back in March. Even if Thornton doesn't seek direct revenge for that insult, there's plenty of possibilities for fireworks with the Blackhawks adding physical players like Daniel Carcillo, Jamal Mayers, Steve Montador and Sean O'Donnell this offseason to a squad that already possessed 6-foot-8, 258-pound heavyweight John Scott.
The puck drops at 8:30 p.m. ET in Chicago, so check back here for updates on all the action.