Milan Lucic added two goals and an assist for Boston, while David Krejci had a goal and two assists. Shawn Thornton also scored and Patrice Bergeron added three assists for the defending Stanley Cup champions, who seem to be finding their game after a sluggish start to the season.
With starting goalie James Reimer still out with concussion-like symptoms, Ben Scrivens was unable to repeat his stellar NHL debut Thursday when he stopped 38-of-39 shots in Toronto's 4-1 win at Columbus. The Leafs rookie allowed five goals on 14 shots against the Bruins, who have won two in a row for the first time this season.
Scrivens was replaced by Jonas Gustavsson after the fifth Boston goal. He was jeered by the crowd in the third period after the seventh Boston goal.
The Bruins took control early in the second when Seguin and Lucic scored eight seconds apart.
Seguin gave the Bruins a 2-0 lead just 34 seconds into the middle period with a great display of hand-eye coordination. The 19-year-old batted a deflected pass from Bergeron past a helpless Scrivens.
Lucic stretched the Boston lead to three moments later off a great feed from Zdeno Chara. The Bruins captain found Lucic with a tape-to-tape pass up the middle off the face-off at center and the hulking winger split the Toronto defense before firing a shot over Scrivens' shoulder.
Toronto coach Ron Wilson used his timeout after the goal, but it did little to stop the Boston tide, as the Bruins continued to dominate play.
Seguin, who took a big hit from Joey Crabb earlier in the period, completed his hat trick at 15:01 when he beat Scrivens with a snapshot shortside and Krejci made it 5-0 just 14 seconds later off a feed from Lucic.
That was the end of a disappointing night for Scrivens, who flew in family and friends from Alberta to see his first home game with Toronto.
Lucic made it 6-0 off a pass from Krejci at 5:44 of the third and Thornton banged home his first of the season for Boston's seventh 28 seconds later as boos rained down from the Air Canada Centre crowd.
Seguin, drafted second overall by the Bruins with one of the picks acquired in the Phil Kessel trade, showed Maple Leafs fans his talent on a big stage. Kessel, meanwhile, continued to struggle against his former team, registering just two shots.
Kessel has 10 goals and 11 assists on the season. He's been held pointless just three times, including twice against Boston.
The Bruins started the season 3-7-0 but beat Ottawa on Tuesday after back-to-back losses to Montreal and defeated another Northeast Division opponent in Toronto to get out of last place in the Eastern Conference.
Boston took the lead on the power play at 6:23 of the first. With Crabb off in the box for holding, the Bruins worked it around nicely to Seguin, who fired a one-timer past Scrivens from the right face-off dot.
A sluggish opening period was a sign of things to come for the Leafs, who only got their legs moving as the period wore on. Jay Rosehill had a puck skip over his stick in front and Nikolai Kulemin couldn't find the range off a scramble with Thomas out of position.
Boston finished the night 1-for-2 on the power play, while Toronto was 0-for-3.
Notes:
D Luke Schenn, C Philippe Dupuis and RW Colton Orr were scratched by the Maple Leafs. … D Steven Kampfer and LW Benoit Pouliot sat out for Boston. … The Leafs wore their heritage jersey. … The Bruins spent Friday at the Hockey Hall of Fame signing autographs for fans. The team will also donate a Stanley Cup ring to the Hall. … Toronto C Tim Connolly needs one more point for 400 in his career.