The spotlight certainly was on Mavericks star Cooper Flagg when he took the floor at TD Garden on Friday night for his first pro basketball game in Boston.

But the night didn’t belong to just Flagg, a Maine native who grew up cheering for the Celtics and drew loud ovations from family, friends and fans who made the trip down to see him. The 19-year-old had to share the stage with Celtics star Jayson Tatum, who made his highly anticipated return after rupturing his Achilles last May.

That was more than fine with Flagg, though, given his special relationship with Tatum.

“It’s incredible,” Flagg said following the 120-100 loss to the Celtics. “There were so many levels to it. He was somebody I idolized growing up and watched him go through levels and ranks and watched him at Duke. Kind of been following in his footsteps, go and play for (Jon) Scheyer at Duke, and then obviously coming into the league. This is surreal. It’s really special just for me to have this experience.”

It didn’t take long for Flagg and Tatum to become face-to-face on the court. Right off the opening tipoff, Flagg found himself guarding Tatum on the wing. But at that point, it was all just about basketball for the teenage phenom.

Flagg ended up scoring 16 points on an inefficient 7-for-23 shooting while also totaling eight rebounds, six assists and three turnovers in 30 minutes. It was just Flagg’s second game back — on the second night of a back-to-back, too — after missing eight straight games due to a left midfoot sprain.

Flagg and Tatum got to have another on-court moment, albeit a brief one, once the final buzzer sounded. Flagg and Tatum embraced and both shared words of encouragement for one another.

“He just told me to keep going,” Flagg said. “He’s been a mentor for me through my journey from Duke to now. He’s somebody I’ve been able to talk to and get advice from. He’s just being a mentor, he just told me to keep going and I told him the same. I told him that it’s incredible what he was able to do and how quick he came back. It’s really incredible.”

Flagg is just 51 games into his NBA career. The 6-foot-9, 205-pound forward with a stellar all-around skillset that made him the No. 1 overall pick in last year’s draft has a long way to go to gain the same status Tatum has in the league as a perennial MVP candidate.

But Flagg has followed Tatum’s blueprint up to this point, and don’t expect him to stop now.

“It’s just getting better. He shared that with me,” Flagg said. “I went to his camp when I was younger. Just learning some of that stuff from him and his work ethic and some of the things that make him so special and try to learn the best I can from him.”