With much of the attention focused on Philadelphia young guns Simmons and Joel Embiid, Boston’s youth movement of Tatum and Rozier led the way. Rozier, in his third year, added eight rebounds and six assists, and Al Horford had 26 points and seven rebounds for Boston.

Embiid scored 31 points with 13 rebounds for Philadelphia. Simmons, the likely rookie of the year, scored 18 with seven boards and six assists.

Game 2 is Thursday night in Boston.

The Celtics are hoping to have guard Jaylen Brown back from a hamstring injury he sustained in the first-round series against Milwaukee. He had been “very doubtful” for the second-round opener and was ruled out about a half hour before the tipoff, adding to injury woes that had already cost Boston Gordon Hayward and Kyrie Irving.

Playing point guard in place of Irving, Rozier was a star for Boston in Game 7 against Milwaukee and he came out hot again against the Sixers. He had 10 points and six assists in the first quarter and was 7 for 9 from 3-point range overall, overshadowing the lottery picks accumulated by Philadelphia during The Process.

The first overall pick in the 2016 draft who sat out all of last year with an injury, Simmons was heckled by the Boston crowd with chants of “Not a Rookie!” In the fourth quarter, as Tatum stepped to the free throw line to protect a double-digit lead, the chant turned to “He’s a Rookie!”

Tatum was Boston’s first pick last year — third overall — after swapping the No. 1 pick to the Sixers and grabbing a 2018 first-rounder as well. Philadelphia picked Markelle Fultz; he did not play on Monday night.

It was 33-all with just over seven minutes left in the half when the Celtics ran off 10 points in a row. Horford had four of the five baskets and assisted on the other. Boston led 87-70 in the final minute of the third quarter when Philadelphia scored nine straight points to make it a nine-point game.

After Simmons made a layup to make it 97-88, Horford hit a 3 from the top of the key with 5:30 left and it was never within single digits again.

OLD SCHOOL FEEL

Sixers coach Brett Brown is familiar with the Philadelphia and Boston matchups of the 1980s, having grown up in South Portland, Maine. Though he knows other teams in the East remain relevant, he thinks there is enough young talent on the current 76ers and Celtics rosters to give the rivalry a rebirth.

“I hope so,” Brown said. “I personally grew up with this rivalry, just right on your doorstep and just a big part of your basketball life as a young kid. It sure seems like both programs are heading into the right direction.”

TIP-INS

Sixers: With six days off since eliminating the Heat in five games, the Sixers missed 15 of their first 20 shots. … Simmons grew frustrated near the end of the game when Shane Larkin wrapped him up under the basket. The Celtics guard gave him a bear hug from behind to prevent him from shooting, and Simmons pushed his hands away. … Embiid again wore the mask he has needed since missing 10 straight games — including the first two of the playoffs.

Celtics: Hall of Famer and 11-time NBA champion Bill Russell was in the crowd…. Smart missed his first five shots. … The Celtics put T-shirts on every seat that said “BEAT PHILA.” The “L-A” were in bold, a nod to the longtime rivalry with the Lakers.