PHOENIX

Jayson Tatum got the better of Josh Jackson in a showdown of two of the top four picks in last year’s NBA draft.

Tatum scored 23 points, Marcus Morris had 20 points in three quarters before leaving with an injury and the Boston Celtics rolled over the Phoenix Suns 102-94 on Monday night.

Tatum surpassed 1,000 points for the season, and Boston won its fourth straight to move to three games behind the Toronto Raptors for first place in the Eastern Conference.

The game featured two young talents who are getting major minutes. Tatum was the third pick in last year’s draft, and Jackson, the fourth pick, led the Suns with 23 points. Jackson has scored 15 or more points in seven straight games, but the Suns lost their 12th straight and have dropped 27 of 29.

“I’ve known Josh for a long time,” Tatum said. “It’s always fun to compete. When you get more opportunities and you’ve got somebody that can play, they’re going to show what they can do.”

Morris, a former Sun, re-injured a sprained right ankle that forced him out of the Celtics’ game Sunday at Sacramento. He didn’t play in the fourth quarter.

Al Horford added 19 points, nine rebounds and seven assists for the Celtics.

“In my eyes, he’s the rookie of the year,” Horford said of Tatum.

Tyler Ulis added a season high 19 points for Phoenix.

The Celtics were without star guard Kyrie Irving, who had knee surgery Saturday. The Suns were without their star guard, Devin Booker, who missed his fifth straight game with a hand injury.

Tatum scored nine of the Celtics’ first 11 points, while Jackson had all of the first 11 for the Suns. The Celtics made 5 of 7 3- pointers in the first quarter and led 31-15 when it ended.

Boston led 39-19 during the second quarter, but the Suns chipped away and cut the lead to 48-45 on Marquese Chriss’ rebound basket with 5.6 seconds to go until halftime.

“As soon as we went to the bench I thought our guys did a real good job for us,” Suns coach Jay Triano said. “Changed our energy in the game. They got up and they pressured, followed the game plan.”

Boston made 7 of 21 second quarter shots while Phoenix went from 24 percent in the first quarter to a field-goal percentage of 55 in the second. Ulis spurred the comeback with seven points, five assists and four rebounds in the quarter.

“Just playing free and playing with confidence,” Ulis said.

The Suns tied it at 56, but Morris’ three free throws after the third quarter buzzer gave the Celtics a 77-65 lead. He aggravated his ankle injury on the foul.

“It’s just sore,” Morris said after X-rays came back negative. “Be out a couple of days but nothing long-term.”

The Celtics were never seriously threatened in the fourth.

BOOKER BEING AROUND — Triano was asked how Booker is doing from a leadership standpoint while still sidelined.

“He’s been active in practice and going through drills with us and just trying to keep his hand out of the mix and verbal on the bench,” Triano said. “His basketball IQ is so good, he’s got a lot of that he can rub off on people.”

TIP- INS — Celtics: C Greg Monroe, a Sun for 20 games earlier this season, scored eight points in 19 minutes. … Horford had the most impressive blocked shot of the night, swatting Jackson’s first-quarter drive into the seats. … Seattle Mariners All-Star 2B Robinson Cano attended the game.

Suns: Fan favorite Alan Williams made his season debut with the Suns and played 16 minutes. He had right knee surgery in September, came back and spent the past week in the G-League with Northern Arizona. … F T.J. Warren missed his fourth straight game with left knee inflammation. … Chriss skied above the rim to send home a two-handed dunk off a lob from Ulis in the second quarter.

UP NEXT — Celtics: At Utah Wednesday night.

Suns: Host L.A. Clippers Wednesday night.