PHOENIX -- Rookie guard Tyler Ulis capped the best day of his career with his first walk-off game-winner.

The Phoenix reserve scored a career-high 20 points, and his 3-pointer from deep on the right wing as time expired gave the Suns a 109-106 victory over the Boston Celtics at Talking Stick Resort Arena on Sunday.

Eric Bledsoe tied the game on a layup with four seconds remaining, and after Marquese Chriss slapped ball away from Isaiah Thomas on the inbounds play, it rolled right to Ulis.

"'Quese' made a big play," Ulis said. "He harassed Isaiah trying to slow him down and ended up getting a steal. It fell into my hands, and I had to let it go with confidence. It feels great. They're a playoff team."

Ulis, a second-round pick from Kentucky, made 8 of 12 field-goal attempts and added five assists. He had 17 points at halftime, surpassing his career high of 14, and scored 11 consecutive Phoenix points in once stretch.

"Tyler Ulis. No more questions. Thanks for coming," Suns coach Earl Watson said to open his postgame media conference.

Bledsoe had 28 points, Devin Booker had 16, TJ Warren had 14 and rookie Chriss had 10 points and a season-high five blocked shots as the Suns (21-42) won a third straight for the first time this season.

Thomas had 35 points and five 3-pointers, and Jae Crowder contributed 16 points and 10 rebounds for the Celtics (40-23). Boston had a two-game winning streak broken.

"I thought Jae would get (the inbounds pass) out quicker than he would," Thomas said of the final play. "Then I looked away, looked back, and Marquese was there and he got a hand on it. I couldn't get full control of it."

Jaylen Brown and Thomas hit back-to-back 3-pointers to give the Celtics a 93-91 lead with 4:41 remaining, Boston's first lead since the second quarter, to begin a back-and-forth that included eight lead changes in the final 2:42.

Thomas made a driving layup for a 101-100 lead before Alan Williams sank a follow shot with 50.9 seconds left to put the Suns up 102-101.

Crowder made a driving layup and the ensuing free throw for a 104-102 lead with 41.6 seconds remaining. After a Suns miss, Brown made a free throw and Bledsoe hit a layup with 13.7 seconds to go, cutting Boston's edge to 105-104.

Thomas made one free throw with 11.2 seconds remaining before Bledsoe's layup with four seconds left.

"This is what I've always wanted as a player, to be in this spotlight, to be in the NBA," said Ulis, who has received extensive playing time as the backup point guard since the All-Star break. "I'm taking on the challenge and trying to be aggressive offensively and defensively."

Williams had 11 points and 15 rebounds, his third straight double-double.

Thomas made 10 of 25 field-goal attempts, 5 of 12 from 3-point range, and all nine free-throw attempts.

Brown and Amir Johnson had 13 points apiece for the Celtics.

Ulis scored 15 first-half points. He made four free throws in the final minute of the second quarter as the Suns used a period-ending 22-7 run for a 49-42 halftime lead. Phoenix's edge grew to 79-64 in the third quarter before the Celtics came back.

NOTES: Celtics F Al Horford (right elbow sprain) and G Avery Bradley (right hamstring strain) missed the game. Horford had 17 points in 31 minutes against the Los Angeles Lakers on Friday. Bradley previously missed about two months with an Achilles tendon injury. ... Suns C Tyson Chandler and G Brandon Knight each missed a sixth consecutive game as the Suns have opted to give extended minutes to rookies G Tyler Ulis and F Derrick Jones Jr. and second-year C Alan Williams. ... Suns G Devin Booker and Boston G Isaiah Thomas are the only two players who have scored at least 24 points in multiple quarters this season. Each has done it twice. ... The Suns improved to 13-9 against the Eastern Conference.