Cooper Flagg starts for the Dallas Mavericks against the Boston Celtics tonight at TD Garden, with tipoff set for 6 p.m. EST.
Without Kyrie Irving, who is out with knee management a night after losing in Cleveland, Dallas leans harder on its sophomore forward against a Boston team riding five straight wins.
Flagg, 19, grew up in Newport, Maine, in a household built around the Celtics. His mother, Kelly, captained the University of Maine basketball team, his father, Ralph, built his college career at Eastern Maine Community College, and twin brother Ace plays at Maine now.
Basketball was the soundtrack on the road, too. During long drives to practice, the Flagg twins put on a disc of the 1985-86 Celtics, the title team of Larry Bird.
Dallas made him the No. 1 pick in 2025 after one season at Duke, where he averaged 19.2 points, 7.5 rebounds and 4.2 assists. He then won Rookie of the Year, putting up 21.0 points, 6.7 rebounds and 4.5 assists over 70 games. This season he is averaging more than 24 points a night with about seven rebounds and more than six assists. On Saturday in Cleveland, Flagg added 18 points with eight rebounds and five assists across 38 minutes without a turnover, while Irving scored 34 in the loss to the Cavaliers.
Cooper Flagg’s Record Against the Boston Celtics
Flagg has faced Boston twice, and Dallas lost both. On Feb. 3 in Dallas, he posted 36 points, nine rebounds and six assists in a 110-100 defeat, becoming the first teenager with three straight 30-point games.
The sequel was rougher. In his TD Garden debut on March 6, Flagg shot 7 of 23 from the field and missed all four of his 3-point tries, finishing with 16 points, eight rebounds and six assists in a 120-100 loss. He had also played Thursday, and Friday’s game was only his second game back from a foot sprain. Across both meetings, he averages 26.0 points, 8.5 rebounds and 6.0 assists.
Maine traveled to Boston in force that night, and Flagg drew the second-loudest ovation during pregame introductions, trailing only Jayson Tatum.
The building is the one Flagg visited as a kid.
“It’s a dream come true, just being out there on that court,” he said, according to the Bangor Daily News.
The question of Flagg someday wearing Celtics green came up that night, too.
“Nah, I love being a Maverick,” Flagg said, according to Boston.com.
Flagg has said he modeled part of his game after Tatum, who played at Duke before him.
“I’m excited to face off and compete against him for sure,” Flagg said before their first meeting.
Boston Celtics, Dallas Mavericks Starting Lineups With Cooper Flagg
Tatum, a 6-foot-8 forward, went No. 3 in 2017 out of Duke, the same one-and-done path Flagg followed in 2025. In March, Tatum made his season debut after an Achilles tear and finished with 15 points, 12 rebounds and seven assists in 27 minutes. Tatum is averaging 26.3 points for the 10-2 Celtics now.
Missing from Boston’s side this time is Jaylen Brown, who scored 33 points against Flagg and Dallas in February. The Celtics traded Brown to Philadelphia for Paul George in July. Boston’s Sam Hauser has called Flagg a strong mid-range scorer and pick-and-roll player, and said New England has embraced him, down to the New Balance billboards.
The Celtics start Derrick White, Jordan Walsh, Paul George, Jayson Tatum and Neemias Queta, according to NBC Boston.
Dallas counters with Naji Marshall, Caleb Martin, Flagg, P.J. Washington and Daniel Gafford.
Boston has won 11 of its last 13 against Dallas, a stretch that includes the 4-1 Finals victory. The Mavericks are 0-2 this season when Irving sits. Flagg is 0-2 against Boston.
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