The Philadelphia 76ers continue to ride the James Harden Rollercoaster, a white-knuckle situation if ever there were one. The Boston Celtics appear to believe that time can be made to stand still. It is altogether fitting and proper, then, that an Eastern Conference semifinal series featuring two such flawed teams is deadlocked at two games apiece.

Somebody’s gotta win what is now a best-of-three set, which resumes Tuesday in Boston.

Or, more to the point, somebody’s gotta lose.

While Boston retains homecourt advantage, it’s hard to discern which team truly has the edge. Both carry those Greg Kite-sized question marks. Neither seems capable of putting a stranglehold on this thing at present.

It was the Sixers who prevailed in Sunday’s Game Four, 116-115 in overtime, as Harden capped a masterful 42-point performance by nailing the decisive 3-pointer with 18.2 seconds left in the extra period.

Yes, you read right – 18.2 seconds remained. An eternity, as we have often been reminded.

And here is what happened (or did not happen) next. Rookie head coach Joe Mazzulla did not call a timeout, which would have enabled his team to inbound the ball at midcourt. Rather, Marcus Smart dribbled the ball upcourt, slowly. He stopped beyond the top of the circle, dribbled a couple more times and finally, with about eight seconds remaining, passed to Jayson Tatum on the left wing.

Tatum likewise hesitated, before attacking the rim with just over five seconds left. He surged through traffic, emerged to the right of the hoop and passed to Smart, who had spotted up beyond the arc on the right wing. Knowing little time remained, he hoisted his 3-point attempt, and while it found the bottom of the net, it was clearly late.

“That was the play,” Mazzulla said later. “We just had to play with a little more pace,”

Ya think?

The C’s seem like the better team. They are younger, deeper, faster and better-balanced. But they frittered away a five-point lead in the final two minutes of regulation and a two-point lead in the closing seconds of overtime Sunday, continuing a season-long trend of late-game implosions. They were 4-7 in overtime during the regular season and in Game Five of a first-round series against Atlanta coughed up a 13-point-fourth quarter lead. Maybe such lapses are due to Mazzulla’s inexperience. Maybe they result from the fact that Boston often plays without a true point guard. Whatever the case, something is clearly lacking.

The Sixers, meanwhile, have become more dependent on Joel Embiid and Harden than ever. With Embiid nursing a sprained knee, Harden poured in 47 points in Game One of this series, including the pivotal triple over Al Horford in the closing seconds. But Harden, whose up-and-down play this postseason has been comparable of that of the Lakers’ Anthony Davis, managed just 28 points on 5-for-28 shooting as his team dropped the next two.

“I don’t even remember that,” he said Sunday.

It’s at least possible he was being truthful, given the way he had just played: 16-for-23 from the floor, 6-for-9 from 3, nine assists, eight rebounds, four steals. But again, it seems fair to ask which of these teams can be trusted at this point. One of them is going to move on to the conference finals, and will presumably be favored to reach the Finals.

Does Harden have two more games like this in him? His playoff history would suggest otherwise. Can Embiid, who contributed 34 points and 13 rebounds Sunday, continue to excel on one leg? And can anybody else step up?

Tyrese Maxey, so good in the regular season, was 6-for-17 while scoring 14 points Sunday. He is shooting 37 percent from the floor in the series, his speed having been blunted by Boston’s big, physical wings. Tobias Harris was 3-for-10 in Game Four, and his most useful shot was the airball P.J. Tucker turned into a game-tying three-point play with 1:06 left in regulation.

But the Sixers’ problems might not matter, if the C’s continue to spit the bit down the stretch. For all their talent and experience – you might recall that they held a 2-1 lead over Golden State in last year’s Finals – they’re so disjointed, so odd. Jaylen Brown notched 12 points in the game’s first five minutes Sunday, but finished with just 23. While he went 10-for-16 from the floor, his last field goal came with 6:13 left in regulation. He was limited to a single attempt thereafter, none coming in overtime. 

Tatum, the team’s other primary weapon, missed his first eight shots but finished 9-for-20 for his 24 points. He also provided 18 boards, six assists and four blocks. And it was his 3-pointer with 37.3 seconds left in the extra period that put the C’s up 115-113. It also enraged Sixers coach Doc Rivers, who correctly pointed out that Tatum pushed off on Maxey.

Rivers said it was “awful that that wasn’t called” and added, “I know it’s a big play, and I’m a big fan of refs not deciding (games), but that could have decided the game.”

Rivers will certainly be fined for saying that, but he appeared to have a legitimate gripe. Likewise with a Tucker foul on Smart in the final minute of regulation, and an Embiid charge on Smart in overtime, which could have been a three-point play.

Harden was so good, he erased all of that. Every last bit. He spotted up in the right corner on the game-winning sequence, then saw his defender, Brown, leave him to double Embiid in the post. Embiid found Harden, and his shot was true.

Best-of-three now, then. One of these flawed teams will win. Or, more likely, one of them will lose.