PHILADELPHIA — The Process has been delayed. Stymied. Halted.

The talented, callow Philadelphia 76ers gave away a second consecutive playoff game, 101-98, and with it a series. No NBA team has come back from a 3-0 series deficit.

This one won’t, either.

Not with these kids. Not with this coach.

Not against a toughened, disciplined, well-coached team such as the Boston Celtics.

They’re just not ready. It’s just that simple.

The Sixers hadn’t sniffed the playoffs since 2012. The Celtics went to the Eastern Conference finals last season. At this point in the teams’ developments, the Celtics are too savvy, too deep and too well-run for the Sixers to beat.

Rookie point guard Ben Simmons can’t contend with a team that engineers its game plan to expose his inability to shoot. Second-year center Joel Embiid, who played in only 31 games last season, lacks the repertoire and refinement to carry a team for four quarters. Brett Brown, the South Portland native in his first playoff run as a head coach, can’t get them past a Celtics team whose two best players aren’t even playing. That should tell you all you need to know about how well Brad Stevens is coaching his club by comparison.

This sort of yardstick series is a necessary part of The Process, but that doesn’t mean it hurts any less.

“Joel’s gonna learn a lot. Ben Simmons is gonna learn a lot. It’s painful admitting that now,” Brown said. “But there is some truth to that. There’s a lot of truth to that.”

That said, Brown refused to completely blame his team’s youth.

“We are navigating through this. This isn’t entirely a youthful thing at all. Nobody write that,” he said. “Some of the matchups have hurt us.”

Sorry, but we will write that. The matchups hurt the Sixers chiefly because the Sixers are so young. They’re so young chiefly because The Process – begun five years ago by Brown, former general manager Sam Hinkie and owner Josh Harris – is clearly far from complete.

It took a jump shot at the buzzer to force overtime in Game 3 on Saturday, and, with 1:05 to play in overtime, it appeared the Sixers might, in fact, continue their astounding accelerated development, that they might survive this round despite having lost twice, disparagingly, in Boston.

In Game 1, they blamed five-day rust. In Game 2, they held a 22-point lead but frittered it away as Brown miserly hoarded his timeouts.

In Game 3, they first threw away a chance to win with 4.7 seconds to play in regulation, when J.J. Redick’s pass never found Embiid and Simmons, who collided near the foul line. Jaylen Brown’s layup forced Marco Belinelli’s hero shot.

The Sixers then threw away the game thrice more, all in the last minute of overtime. Leading 98-96, Embiid turned the ball over with 46.6 seconds to play, which let the Celtics cut it to one. Embiid then missed a shot with 20.8 seconds left, even as he insists, “I was built for this moment.”

He wasn’t built for that moment. He’s a work in progress.

Still, Simmons got that rebound – and inexplicably he immediately shot it again (and missed), instead of kicking it out and trying to run out the clock or forcing the Celtics to foul.

The Celtics then scored with 5.5 seconds to play in overtime on an inbounds play on which Brown ordered every player to switch on every screen, which led to small forward Robert Covington defending power forward Al Horford, who caught and shot under the Celtics’ basket. The Sixers still had 3.9 seconds, down by one, but Stevens correctly anticipated the in-bounds play. Horford anticipated a pass to Embiid and stole it when Simmons threw it.

Those plays will weigh badly in the Brown vs. Stevens conversation.

“I’m the coach,” Brown said. “I’ll take responsibility for all of this.”

That seems satisfying in the moment, but it’s wrong to blame Brown for everything. He didn’t build the team.

Rookie forward Jayson Tatum’s 24 points Saturday made him the first Celtics rookie to hit 20 points in five straight playoff games. General Manager Bryan Colangelo traded a future first-round pick to Boston to select Markelle Fultz, who has scored five points in these entire playoffs, zero in the last seven games and hasn’t even played in the last five.

Covington is in his fourth full NBA season, but this is his first playoff run. He scored three points in Game 1, had just one point Saturday, and is 0 of 14 in the two games combined. He’s known as a good defender but he often defends Tatum, so …

Dario Saric, who should have been rookie of the year last season, is shooting 37.1 percent from the field against the Celtics, more than 8 percentage points worse than his season’s average.

Brown is reluctant to blame his players’ inexperience for everything, and he shouldn’t, because he and Colangelo haven’t been perfect, either. But they helped these kids win 52 games in the regular season, including 16 straight to end it, and they waxed the Heat in five to win the first round.

“I don’t like blaming youth. We made mistakes. It doesn’t matter how old we are,” Embiid insisted. “It doesn’t matter we’ve never been in this position.”

Of course it does.

“They showed up in the time when it was the time to show up, and we didn’t,” Embiid continued.

The Sixers will, of course. They will one day.

Just not now.