BOSTON -- Kyrie Irving saw the play unfolding before the rest of the Boston Celtics' bench, and his blazer-clad arm shot skyward, requesting the lob that would soon follow.

The Celtics were breaking out in transition late in the first half of Game 2 of their Eastern Conference semifinal series against the Philadelphia 76ers. As Marcus Morris dribbled down the right side of the floor in front of Irving, the All-Star point guard's eyes were already locked on Jaylen Brown sprinting on the opposite side of the court with only JJ Redick between the Boston players.

So as Morris reached the foul line and lofted the ball toward the rim, Irving shuffled a couple of steps closer to the baseline then crouched a bit on the left knee that required surgery last month and ended his 2017-18 season. It was an injury that was supposed to squash any remaining hopes of an extended postseason stay for these injury-ravaged Celtics.

Then, Brown -- a game-time decision with the sore hamstring that kept him out of Game 1 -- rose up and threw down a two-handed slam that threatened to dislodge TD Garden from its foundation. It capped a violent and completely improbable late-first-half run that spearheaded Boston's comeback from a 22-point deficit.

And it simply felt like there was no way the Celtics were not going to complete their comeback after that.

Rookie Jayson Tatum scored a team-high 21 points, while Terry Rozier had 20 points, 9 assists and 7 rebounds as the Celtics overcame the big deficit and then found the energy for one more fourth-quarter burst en route to a 108-103 triumph.

Even after the arena had cleared out following Thursday's game, Brown -- who finished with 13 points on 5-of-12 shooting and, despite the hamstring strain, contributed a couple of flashy dunks that worked the crowd into a lather -- marveled at the decibel levels reached during Boston's first-half surge.

"Man, I've never seen TD Garden like it was tonight," he said. "I think I'll remember that game forever. The way the crowd got behind us before the half. That last five minutes, man. The energy was insane. I don't think I'll ever forget that. Like that was the moment to definitely remember. Game 2, Philadelphia, 2018. For sure."

Boston outscored Philadelphia 50-20 during one 16-minute stretch spanning from midway through the second quarter to late in the third frame. What made that run all the more wild was that it seemingly came out of nowhere for a Boston team that needed nearly the first 18 minutes of the game to total 26 points -- then essentially doubled its output over the final 6:20 of the half.

Then came the deluge. And fans that had plenty of time to get primed for the unusually late 8:42 p.m. ET tip time were more than happy to revel in the comeback.

Their energy helped power the Celtics.

"You feel it a lot. Like, oh my gosh," Celtics big man Al Horford said. "You're out there, you're exhausted, you're tired. But when the Garden is rocking like that, it's something, you just can't quit. You just want to keep it going, you want to keep riding it. You don't want to be in that position [of playing from behind], but you are, and we keep finding a way. We keep fighting."

The Celtics lost Gordon Hayward to a season-ending ankle injury during the season opener in Cleveland, then saw Irving's balky knee require season-ending surgery in April, but they have somehow kept themselves afloat while navigating tumultuous seas.

And now Boston, with its young roster, is two games away from a return trip to the Eastern Conference finals. How exactly are these Celtics doing this?

"It's kinda funny, we've been getting the same question since the first game of the year. You know what I mean?" Brown said. "And we're here in what, May? Is it May? And still getting the same question.

"Man, we just play basketball. We got a great coach in Brad Stevens, we've got a great front office in Danny Ainge and his crew, and we got some really tough talented guys in this locker room. When you put that three together, that's what makes success."

The Sixers had promised they wouldn't shoot as poorly as they did in Game 1, and, true to their word, they blitzed the Celtics with a 3-point barrage. Redick scored the first eight points of the game and hit three first-quarter 3-pointers as the Sixers opened a double-digit advantage.