Westbrook on Sunday saw his streak of consecutive games with triple-doubles end at seven as he shot 14-of-26 and tallied 12 rebounds and six assists in front of a crowd of 18,400 at Chesapeake Energy Arena.
"We have got to be able to close the door," Westbrook said. "We are not going to be able to blow teams out like we used to. We have got to grind it out."
Steven Adams added 16 points and eight rebounds for the Thunder who improved to 15-9. Enes Kanter came off the bench to score 14 points.
Al Horford led Boston with 19 points and six rebounds. Jae Crowder and Avery Bradley each finished with 18 points as Boston dropped to 13-11.
Westbrook, who leads the NBA in fourth quarter scoring, had 13 in the quarter.
"I'll say this about the triple-doubles, because I always find this interesting," Thunder coach Billy Donovan said.
"On a night like tonight, does it make it any less special if he had a couple of more assists. He did a lot of different things that impacted the game at a high level."
With 3:20 left in the fourth, Oklahoma City's Adams completed a three-point play to cut the deficit to 90-89. Bradley responded with a jumper on the other end.
Westbrook then sank a three-pointer to tie the game. But once again Bradley answered with a basket off a missed shot.
Westbrook tied the game with 1:20 remaining in the fourth. Boston gave the ball to Horford, but he had his shot blocked by Adams.
The Thunder got the ball with 39 seconds left and Westbrook carried down the lane to the front of the rim for a layup and Oklahoma City grabbed a 96-94 lead.
Westbrook won a tip ball and tapped it ahead to Anthony Morrow. He pushed it to Jerami Grant for an impressive two-handed dunk with 14 seconds left in the game.
The Celtics were able to cut the lead down to two, but Westbrook nailed one-of-two free throws. Marcus Smart had a chance to tie, but his three-point attempt missed.
In Minneapolis, the Golden State Warriors rebounded from a road loss to beat the rebuilding Minnesota Timberwolves 116-108 and extend their NBA-record streak of not losing back-to-back games.
The Warriors delivered in the fourth quarter to fend off the Timberwolves and make sure their 111-game streak of not losing consecutive regular season games continued.
"It's really one of the most impressive streaks that I've ever seen," said Warriors coach Steve Kerr. "That's a lot of games."
One night after a road loss to the Memphis Grizzlies, Golden State trailed by 10 after three quarters but outscored Minnesota 38-20 in the fourth to pull away for the win.
Golden State began the fourth quarter with a 25-4 surge. Warriors guard Klay Thompson scored 12 of his 30 points during that fourth-quarter run.
Kevin Durant added 22 points and eight rebounds, Stephen Curry had 22 points and nine assists, and Draymond Green scored 18 for the Warriors, who improved to 21-4.
Minnesota's Karl-Anthony Towns tallied his 15th double-double of the season with 25 points and 18 rebounds.
In Detroit, TJ McConnell had 12 points and 10 rebounds and finished one assist shy of a triple-double as the Philadelphia 76ers defeated the Detroit Pistons 97-79.