Instead, they turned it into the easiest one their current group has ever experienced.
Kevin Garnett had 26 points and 10 rebounds, Rajon Rondo added 21 points and 12 assists, and the Celtics swept their way into the Eastern Conference semifinals, holding on for a 101-89 victory over the New York Knicks on Sunday.
Ray Allen and reserve Glen Davis each added 14 points for the Celtics, the first team into the second round after sweeping a series for the first time since a 3-0 victory over Indiana in 1992, the last series victory for their old Big Three before Larry Bird retired.
"It's what we expected coming in. We knew it wasn't going to be easy, obviously Games 1 and 2, but we found a way to put it away," Rondo said. "We haven't swept a team in a long time, so it's good feeling."
And it gives their aging group plenty of rest before an expected showdown with the Miami Heat.
The Celtics had a 23-point lead cut to four in the fourth quarter, but pulled away again behind Garnett, who scored 20 after halftime.
The current Big Three of Garnett, Allen and Paul Pierce twice was extended to seven games in the first round, but this one was far easier than expected against the injury-weakened Knicks. The Celtics could now have a week off while they wait for likely opponent Miami, which was forced to a fifth game earlier Sunday after a late rally by Philadelphia.
The Celtics almost faced the same scenario, but a Knicks comeback attempt stalled in the final minutes before they were saluted by their orange-clad crowd after delivering the best season in New York in a decade.
"Everybody understood what was at stake. Give a team some confidence, even in a 3-0 series to win a game, you never know what can happen," Pierce said. "So it was just very important for us to withstand the run. They made a great run and the crowd really got behind them, but in the fourth quarter we just really settled down in the last six or seven minutes, executed the offense and were able to put the game out of reach."
Carmelo Anthony had 32 points and nine rebounds, and Amare Stoudemire, who decided to play after his back felt better, finished with 19 points and 12 boards but shot only 5-of-20 from the field.
"It was all heart. He just gave it all. With him and Carmelo going forward, the Knicks are in good shape," Knicks coach Mike D'Antoni said.
The Knicks shot 34 percent and were quickly dispatched in their first playoff appearance since 2004, when they were also swept in the first round. They haven't won a playoff game in 10 years.
"Tonight was one of those games that we have to leave it all out on the court. Wasn't no need to take anything home with us, and we did that," Anthony said. "So I'm pretty sure that we gained a lot of respect from a lot of people right now, but this is the first step of something great."
The Celtics were only 10-11 in their last 21 games of the regular season, struggling to adjust to a changed lineup after trading center Kendrick Perkins to Oklahoma City at the deadline and renewing questions they were too old.
The Knicks believed they could challenge them, but Chauncey Billups was lost for good after straining his left knee in the final minute of Game 1 and Stoudemire was never the same after hurting his back during warmups before Game 2.
Meanwhile, the Celtics got better as the series went along, pulling out two close victories in Boston and saving their best for Madison Square Garden, surrounded in orange as it was finally open for postseason basketball again.
But that couldn't shake the Celtics, who held the Knicks to three field goals in the second quarter to seize control.
Garnett made three straight field goals to make it 70-48 in the third quarter before the Celtics let the Knicks back into it. Consecutive run-out dunks by Anthony cut it to 14, and New York had it all the way down to 10 when Shawne Williams' 3-pointer with 36 seconds remaining trimmed it to 82-72 after three.
Stoudemire opened the fourth with a basket and Anthony followed, bringing it within six and forcing coach Doc Rivers to put Garnett back into the game. He made a pair of free throws, but baskets by Stoudemire and Anthony Carter made it 84-80 with 7:34 to go.
"I thought we dropped the guard a little bit," Rivers said. "Give them credit, I thought they played desperate and you could see it in their play and their defensive energy."
But Boston would never let it get closer and finally put it away when consecutive jumpers by Rondo and Garnett extended it to 95-85 with 4:22 to play.
Disappointed in their effort in a blowout loss Friday, the Knicks showed plenty of fight. Anthony knocked Rondo down for a flagrant foul and Stoudemire was called for a technical after he shoved Delonte West in the back following the Boston guard's hard foul on Knicks rookie Landry Fields.
But New York, which went 42-40 to end a franchise-worst streak of nine straight losing seasons and earn its first playoff berth since 2004, simply didn't have enough to match Boston, which got 13 points from Pierce.
Stoudemire made only one field goal in the first half as Boston led 55-38.
D'Antoni, while saying Rondo is a "very good basketball player," seems to feel his success is due more to the players around him. "I'd like to see him play on Minnesota and see how he does," D'Antoni said before the game. "Everybody's tied together and they have three Hall of Famers out there." … Billups said sitting out was "torture." … Kemba Walker, who led Connecticut to the NCAA championship, attended the game and sat with Mayor Michael Bloomberg.