The Sixers struggled to find their rhythm in Joel Embiid’s return. After a Game 2 stinker, they need to find it fast.

BOSTON — Well, there goes the sweep.

To a certain extent, you couldn’t have been surprised by what you saw at TD Garden on Wednesday night. Regression to the mean is a real phenomenon. So, too, is dopamine burnout. And home-court advantage.

We could go on, but you get the gist. There were a whole host of variables that suggested the Celtics were a good bet to bounce back from a Game 1 loss and even this Eastern Conference semifinals series at one game apiece. What you could not have foreseen was the extent to which the 76ers unraveled. That’s where their 121-87 defeat in Game 2 gets a bit concerning.

There are postseason losses, and then there are postseason losses where Jaden Springer and Payton Pritchard are on the court with eight minutes remaining in the fourth quarter. This was the latter of those, and one look at the box score is all you need to know why.

If there were any positives, we’re going to have to rewatch the tape to find them. Maybe a few times. Maybe backward. With with a couple of bottles of wine and some hallucinogens.

That’s how bad this thing was. You could call it a nothing burger, except there was definitely something between the bun. It smelled too awful to overlook. It’s not often that a playoff game leaves you with nothing constructive to say, but Wednesday was one of those nights. Forget watching the film. They might be better off burning it.

“We knew obviously after Game 1 that they were going to come out here with more energy and more pop overall,” Sixers forward Tobias Harris said. “And they did. They got pretty much every 50/50 ball that was out there, hustle plays, offensive boards that led to open threes. For us, there were too many empty possessions that didn’t result in a made shot, which allowed them to get out and run and had us on our heels.”

As Harris noted, some of this was to be expected. In Game 1, the Sixers won a game they had no business winning, and they did it in a fashion that is incredibly hard to replicate. Harden’s 45-point outburst was an all-time great performance. That kind of thing rarely happens two games in a row.

Likewise with Embiid. The Sixers had spent 10 days adjusting to life without their offensive centerpiece. As recently as a few days ago, coach Doc Rivers was assuming he would not have his big man for either of the first two games of the series. His return in Game 2 meant a dramatically different style of basketball than they’d played in their Game 4 win in Brooklyn and their Game 1 win against the Celtics. It also meant playing that style of basketball with a big man who at times seemed conflicted between being himself and figuring out how much of himself he could be.

» READ MORE: Joel Embiid wants his MVP story to serve as inspiration: ‘Improbable doesn’t mean impossible’

That last part remains an open question. On the one hand, Embiid’s 15 points and 4-of-9 shooting from the field were hardly commensurate with the amount of time the ball was in his hands. On the other hand, his mobility and conditioning looked better than you probably would have expected it to look given that he was playing on a 4-to-6-week knee injury two weeks after he suffered it. He was on pace for his typical workload before the game got out of hand, having logged 27 when he checked out of the game for good with 2:19 remaining in the third quarter and the Sixers trailing, 83-62.

Most encouraging was his performance on the defensive end, where he blocked five shots and altered numerous others against a Celtics team that had gotten to the rim with ease in Game 1.

“Yesterday was the first day I really did something going up and down the court in two weeks, so I was pretty surprised,” Embiid said of the way his body responded. “But then again, I said it earlier, I’ve grown a lot and I’ve found ways to take care of myself and kind of know what to do. Obviously, there’s nothing like actually playing a game and finding your rhythm. So at times you kind of feel tired. I thought tonight was fine, but should be better as the days go on.”

From the biggest of big picture perspectives, the Sixers head back to Philly as winners of the first act of this series. If you’d been told that Embiid would miss Game 1 and score 15 points in Game 2, you would have been thrilled to learn that the Sixers earned a split.

The big question is their rhythm. Either Embiid needs to find his fast, or the Sixers need to find a way to feed off somebody else. That’s a lot to ask. It’s also the reality of the situation. The NBA isn’t suddenly going to add any more days between the games. By the time Game 2 ended, the Sixers were less than 48 hours away from the next one. Tune in Friday. It is shaping up to be the game that tells us the tale.

» READ MORE: James Harden carried the Sixers over the Celtics like Allen Iverson vs. the Lakers. Can he do it again?