Irving scored Boston’s first six points in the extra period, and Marcus Morris finished with 17 against his former team — including the tying 3-pointer with 1.1 seconds left in regulation off a pass from Irving.

Morris hit from the top of the arc to tie it at 100. Jaylen Brown added 17 points, all after halftime, for the Celtics.

Devin Booker paced the Suns (2-9) with a season-high 38 points, and T.J. Warren had 29.

Booker scored 12 points in the fourth quarter but Phoenix couldn’t hold onto a 15-point lead to begin the final period.

The Celtics ended a two-game skid, while the Suns have lost nine of 10.

Boston recovered from an ice cold start and won despite shooting 40.2 percent from the field. The Celtics trailed by double digits for much of the second half until a furious late rally.

Suns rookie Deandre Ayton had 14 points and 10 rebounds.

Irving hit a 3 with 35.1 seconds to go in the fourth, then his steal led to Brown’s layup that cut the Suns’ lead to 98-97 with 7.3 seconds to play. Warren hit two free throws, then Morris took a pass from a double-teamed Irving for the tying 3.

Warren, starting for the first time since Oct. 31, scored 14 first-quarter points as the Suns took advantage of the Celtics’ shooting woes. Phoenix led 32-13 after 12 minutes.

After making their first shot of the game, a 3 by Irving, the Celtics missed their next 12 attempts and the Suns raced out to a 15-3 lead.

Aron Baynes’ putback with 5:04 left in the first quarter was the Celtics’ second basket of the game, and they shot just 4 of 22 in the quarter.

Boston got the lead down to 14 in the second, but a 3 from Booker gave the Suns a 48-26 advantage with 4:31 left in the half.

The Celtics trailed 55-35 at the break.

Consecutive baskets by Booker put the Suns in front 75-58 in the third quarter.

TIP-INS

Celtics: Their 13 points in the first quarter were a season low. … Irving was the only starter to make a field goal in the first half. Jayson Tatum, Al Horford, Gordon Hayward and Brown were a combined 0 for 15. … G Marcus Smart surpassed 1,000 rebounds and 400 steals for his career.

Suns: Warren made his third start this season. Ryan Anderson came off the bench. . Booker scored 70 points against the Celtics in Boston on March 24, 2017. . A game after playing a season-low seven minutes, 2017 first-round draft pick Josh Jackson played only five.

ANALYZING AYTON

Celtics coach Brad Stevens called Ayton a “special talent” when asked about the rookie before the game. “He brings everything to the table you would think a really good player at that position brings,” Stevens said.

JAYLEN JAM

Brown’s first basket was a high-flying, one-handed dunk in transition at the 10:10 mark of the third quarter. Smart provided the assist.

UP NEXT

Celtics: At the Utah Jazz on Friday in their second set of back-to-back games this season.

Suns: At the New Orleans Hornets on Saturday.