Sixers coach Doc Rivers needs to figure out James Harden and Tyrese Maxey. Fast.

Phone, keys, wallet ... James Harden?

The Sixers arrived home without one of the above on Friday night. You saw it in the box score. You saw it on the scoreboard. Now you see it in the Sixers’ 2-1 series deficit after a 114-102 loss to the Celtics in Game 3 of their Eastern Conference semifinals. They were a second star short of a fighting chance.

They need to find one quick.

This is Doc Rivers’ big challenge before Game 4: Figure out a Plan B. Maybe it’s Tyrese Maxey. Maybe it’s Tobias Harris. Maybe it’s the sort of team ball we’ve seen from the Celtics all series. Whatever the answer, the Sixers can’t afford to spend another four quarters waiting around for Plan A.

Can a two-man game really work if one of the men doesn’t show? That’s the conundrum that Rivers needs to wrestle with in practice on Saturday. The guy with the sprained knee wasn’t the half that was missing. Joel Embiid looked a lot like his old self in Game 3, scoring 30 points and hitting 9 of 19 shots, most of them hard-earned. That was the maddening thing about this game. Embiid just needed some help.

Harden wasn’t just bad. He was an anchor: 3-for-13 from the field, 2-for-7 from three-point range, five turnovers. As bad as those numbers were, the reality was somehow worse.

Forget the misses. The big problem was the abstentions. After missing his first five shots from the paint — two of them blocked resoundingly — Harden went nearly two full quarters without attempting a shot near the rim. There were plenty of occasions when he put himself in position to do so. Rarely did he even appear to consider the option.

“I thought there were a couple of times we came out of a timeout where we really thought we had the lane,” Rivers said. “I thought we were trying to snake dribble more than just go straight down and make plays. You know, that’s something we talked about: getting into the paint with force, with pace. And if they come, let’s make plays. You know, I just didn’t think we did that.”

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In the Sixers’ locker room after the loss, Harden was understandably defensive when asked about the layups he didn’t take.

“I don’t know, I’ve got to watch the game,” said Harden, who finished with 16 points. “But I’m pretty good on basketball instincts. I know when to score, I know when to pass. So I’m pretty sure a lot of them was the right play.”

Problem is, he might be right. The Celtics apparently learned something about guarding Harden after watching the tape of his 45-point outburst in the Sixers’ Game 1 win. When Jaylen Brown blocked him from behind in the second quarter on Friday night, it was Harden’s fifth miss of the night from inside the paint. This, after an ugly Game 2 performance in which he went 1-for-6 from around the rim.

For the last two-plus quarters on Friday night, Harden was a player who had learned a lesson. This included a conspicuous stretch just before halftime where he picked up his dribble just outside the restricted area and frantically looked to pass despite having plenty of elbow room to utilize. The second of these ended in a turnover, one of five that he had in the first two quarters of play.

This continued through the second half. It was a problem, and the whole building knew it. Late in the fourth quarter, with the Sixers trailing by eight, Harden got to the bucket in what appeared to be scoring position. Instead of challenging the defender, he kicked the ball out. The reaction from the crowd was uncomfortably visceral, a frustrated groan that told you all you needed to know about the game up to that point. A few minutes later, Harden finally muscled home a layup, prompting another roar from the crowd. This time, it felt a bit mocking.

One way or another, Rivers needs to find an answer. Get Harden his confidence back, or get the ball in somebody else’s hands. Some teams can get away with having a point guard who doesn’t shoot. The Sixers are not one of those teams. We saw that in Game 1, when Harden’s 45 points on 30 field goal attempts were the only reason they aren’t currently down 3-0 in this series. The Sixers don’t need that version of Harden, but they can’t survive with the one they had on Friday night.

Maybe there are no good options. You can certainly make that case after watching Maxey shoot just 10-of-30 from the field and 4-of-13 from three-point range in Games 2 and 3. This Celtics team has shut him down for the better part of six straight games now, going back to the regular season. At the same time, Maxey’s struggles look like the kind of thing that some quick coaching can hope to fix. There were plenty of moments in Game 3 when he simply looked like a young player who wasn’t sure if he should take a shot.

“You know, it really is he didn’t get the ball enough,” Rivers said. “And we have to make him get more involved.”

It might be their best chance at altering the complexion of this series. And Game 4 might be their last chance to do so.