PHILADELPHIA (AP) -- As the tension of the game goes up, Isaiah Thomas calms down.
Thomas scored 12 straight Celtics points late in the fourth quarter and tied his season high with 37 points to lead Boston to a 107-106 victory over the short-handed Philadelphia 76ers on Saturday night.
Avery Bradley added 20 points for Boston, which won its ninth straight game against the 76ers.
"I just love the fourth quarter," Thomas said. "Some guys get a little tight, a little timid. I embrace it. I want to be great. I want to be somebody my teammates can call on when the game is close."
The Celtics certainly know they can go to Thomas, who at 5-foot-9 can be described as a little big man. He entered ninth in the NBA in scoring (25.7 ppg) and now has five games of 30 or more points.
"We're a little bit like, 'That's Isaiah,'" Boston coach Brad Stevens said. "But he has a special ability to score the ball. My advice to anybody is buy League Pass and watch him as much as he can because he's a fun guy to watch."
Rookie Dario Saric tied his career high with 21 points while adding 12 rebounds for Philadelphia, which dressed just 10 players. The 76ers lost their sixth straight.
Joel Embiid, who leads the 76ers in scoring (18.7 ppg) and rebounding (7.9 rpg), missed his seventh game as part of the team's rehab plan to not play him on consecutive nights after sitting out the last two seasons with a foot injury.
Thomas scored six straight points to make it 98-91 with 3:05 left. The 76ers scored seven of the next nine to pull within 100-98 with just over a minute left. Thomas' driving attempt was blocked by Jahlil Okafor and then Saric tied it at 100 with 34 seconds left on a layup that just beat the shot clock.
After a timeout, Thomas blew by two defenders for an easy layup that put the Celtics up 102-100 with 30.2 seconds left.
"That's what you see with All-Star point guards," Philadelphia coach Brett Brown said. "He's hard to guard."
Hollis Thompson missed on a drive on Philadelphia's ensuing possession. The Celtics got the rebound and Bradley made one of two free throws with 16 seconds left for a 103-100 lead. Saric's tying 3-point attempt fell short and Marcus Smart made a pair of free throws on the other end.
PHILLY'S FAST START
The 76ers led by as many as 11 points in the opening half before taking a 53-45 lead into the break. The key was 3-point shooting. Philadelphia was 9 for 18 from the arc in the opening 24 minutes while the Celtics were 3 for 11.
Saric had his best game as a member of the 76ers, who acquired him after Orlando selected him 12th in the 2014 draft. He played the last two seasons overseas.
"He was a man down there tonight," Brown said. "You'd walk away and say that's a hell of a player for playing 20 games in the NBA."
Saric provided the highlight of the night when he sent Boston's Jonas Jerebko tumbling to the floor with a behind-the-back dribble before pulling up and draining an 18-footer.
The Celtics entered fifth in the league in both 3-pointers made (11.3) and attempts (31.1) per game. But they struggled from the outside against the 76ers, finishing 8 for 26.
Celtics: This was the first of four meetings between the teams. Boston will host the next two games, on Jan. 6 and Feb. 15, before returning to Philadelphia on March 19. ... Thomas' career high is 38.
76ers: Philadelphia wore throwback jerseys from 1966-67 in honor of the 76ers NBA champions from that season. Billy Cunningham, a player on that team who later coached the 76ers to the 1983 NBA title, rang the replica Liberty Bell during pregame festivities. And many members of the team were recognized in a halftime ceremony.
Celtics: Look to end a four-game losing streak to the Rockets when they visit Houston on Monday night.
76ers: Cap a four-game homestand by hosting Denver on Monday night.