BOSTON -- Celtics fans taunted Philadelphia 76ers forward Ben Simmons with a "not a rookie" chant in the second half of Monday night's Game 1 of an Eastern Conference semifinal series at TD Garden, then came back with a "he's a rookie" chant while Boston's Jayson Tatum was at the charity stripe later in the game.

Tatum, the No. 3 pick in the 2017 draft, scored a postseason career-high 28 points over 40 minutes as the injury-ravaged Celtics emerged with a 117-101 triumph. Tatum joined Larry Bird as the only Celtics rookies over the past 50 postseasons with 25 or more points in a playoff game. Bird did it three times.

Simmons, the No. 1 pick in the 2016 draft who missed all of the 2016-17 season recovering from a foot injury, finished with 18 points, seven rebounds and six assists over 42 minutes.

"I don't care. It doesn't affect me at all," said Simmons, downplaying the barbs about whether he ought to qualify as a rookie this season.

For his part, Tatum said he didn't hear the chants about Simmons. He also downplayed being hyped to play against another top candidate for rookie of the year.

"At this point, I'm just focused on winning, not really matchups," Tatum said. "Just win. It's really a team thing right now."

Pressed on whether he feels he's a better rookie than Simmons, Tatum smiled and paused for a second before offering only, "No comment."

The Celtics have played this postseason without All-Stars Kyrie Irving and Gordon Hayward. Then second-year forward Jaylen Brown was unable to go Monday due to a hamstring strain suffered in Boston's Game 7 win over the Milwaukee Bucks on Saturday.

The lack of typical offensive output meant players like Tatum had to step up. He connected on 8 of his 16 shots and was 11-of-12 at the free throw line. Tatum was plus-18 overall during his floor time.

"Just be aggressive, especially with JB out," Tatum said. "That's 20 points sitting on the bench, and we try to make up for that."

Al Horford offered his take.

"Jayson, he's starting to figure it out," Horford said. "He's understanding what he needs to do, and it's great to see for our team."

Sixers coach Brett Brown offered high praise for Tatum, a player Philadelphia passed on after trading with Boston to secure the No. 1 pick in last summer's draft.

The player the 76ers chose with that pick, Markelle Fultz, was the only player who didn't get off the bench Monday night for the 76ers. Fultz, who returned last month after a 68-game absence for a shoulder injury, also did not play in the last two games of Philadelphia's first-round series against the Miami Heat. Brown said he has gone with T.J. McConnell over Fultz as the backup point guard because he felt McConnell could better handle the physicality and intensity of the playoffs.

Brown said he thought Tatum "was great."

"I think he's had an exceptional year," Brown said. "He's got a bounce. When I watch him, he plays sort of older than his résumé suggests. He's got a lot of bounce and a lot of game. I thought tonight he scored in a variety of ways. I thought he was excellent."

Celtics coach Brad Stevens provided his assessment.

"I thought [Tatum] was really good, really consistent," Stevens said. "He made some tough shots but also got to the rim, made some great plays for us. He got to the line, which we needed, with his drives. I thought he had a good game."