Marcus Smart made a big basket to boost Boston's playoff hopes.
Smart hit a buzzer-beating layup in overtime and the Celtics beat the Toronto Raptors 117-116 on Saturday night.
Boston, which lost at home to Milwaukee on Friday, has won 10 of their past 11 on the second night of back-to-back games.
"It's just the will, the determination," Smart said. "The guys on this team, we're competitors, heavy competitors. We don't like to lose that much, especially when we come off a night where we didn't play that well."
With 2.6 seconds left and Boston trailing by one, Smart took a pass from a driving Isaiah Thomas and sneaked behind the collapsing Toronto defense to score the winning basket, silencing the sellout crowd of 19,800.
"When he drove he committed two defenders, including mine," Smart said. "Lou Williams swiped (the ball) toward the area I was in and I was able to get the shot off in time."
Williams, who'd put Toronto in front with a 3 just seconds earlier, thought he'd secured the win when he got his hands on Thomas' pass.
"I thought I did enough," Williams said. "I figure it's game. I thought I got the stop. It was just a bad bounce."
Thomas scored 25 points, Tyler Zeller had 20 and Evan Turner added 18 points and 10 assists for the Celtics, who moved one-half game ahead of Miami in the race for the final Eastern Conference playoff berth after the Heat lost 99-98 at Detroit.
"We overcame a lot tonight," Turner said. "It was tough. I'm just glad we stuck it all the way through to the end."
Boston moved half a game behind seventh-place Brooklyn, which lost at Atlanta.
The Raptors led 116-115 on Williams' 3 with 4 seconds left, but couldn't hold on. DeMar DeRozan scored 18 of his 38 points in the fourth quarter and overtime, while Williams finished with 27.
Smart had 15 for Boston, while Brandon Bass had 11.
Jonas Valanciunas had 12 points and 14 rebounds for Toronto and Tyler Hansbrough fouled out with 18 as the struggling Raptors lost their second straight. Toronto has lost 15 of its past 23 overall.
Boston led 108-107 after two free throws by Kelly Olynyk and a layup by Turner with 2:44 left in overtime. DeRozan answered with a layup, then stole Olynyk's pass and hit a turnaround jumper to put Toronto up 111-108 with 1:40 left.
Zeller made one of two at the line at 1:06 and, after a missed shot by DeRozan, Smart made a 3 from the corner to put Boston up 114-113 with 32 seconds left. Williams and Terrence Ross both missed 3s for Toronto before Bass was fouled. He made 1 of 2, and Boston led 115-113 with 14 seconds left.
Williams hit a go-ahead 3 to put Toronto back up, but Smart's buzzer-beater gave the Celtics the win.
"You don't win very often with 2.6 seconds," Boston coach Brad Stevens said.
Toronto was without forward Amir Johnson, who sprained his right ankle in Friday's loss at Brooklyn. "His ankle is swollen and he can't walk on it," coach Dwane Casey said before the game." He's out for a little bit."
Also absent for the Raptors was guard Kyle Lowry, who sat for the eighth time in nine games with a sore back.
Boston originally intended to go to Turner on its final possession, but Stevens didn't like the matchup and called a second timeout to draw up the winning play. "I thought it was crazy when we came to the timeout and he already had another play drawn up," Turner said of Stevens. "Obviously what we were looking for originally wasn't open. By the time we got to the timeout he had grabbed the board and everything was drawn up. He was a step ahead."
Celtics: Boston is 12-5 overall in the second game of back-to-backs. ... F Jared Sullinger, who played 3 minutes in Friday's loss to Milwaukee after missing the previous 24 games with a broken left foot, played just over 12 minutes against Toronto. He didn't score but had seven rebounds and drew a charge on DeRozan.
Raptors: Hansbrough started in place of Amir Johnson. ... Boston's 15 points in the first were the fewest by a Toronto opponent this season. The Raptors held the Grizzlies to 16 points in the first in a Jan. 21 loss at Memphis. ...
Celtics: At Detroit on Wednesday night.
Raptors: At Charlotte on Wednesday night.