The moment of doubt for Jermaine O’Neal came at the moment of truth. When the lights go out and the doctor goes to work. He had tried to do everything he could to avoid the surgery -- and took a fair amount of criticism for that decision in the process -- but after all the rehab, all the exercises, he was left with no choice.

The pain in his knee wouldn’t go away, which was a problem, but it was the swelling that prevented him from doing anything on the basketball court. Something had to be done about the swelling.

They call it a scope, which doesn’t sound so bad until you stop to consider the possibilities. What if it goes wrong? What if they find something worse? “That’s the only time that I really had any question whether I could be back,” O’Neal said. “Because you never know.”

A few days later he was walking, which was a surprise to his doctors. Then came the really hard part. More rehab, more work and then, Chicago. “I was never going to be allowed to go to Chicago if I wasn’t passing the tests here,” O’Neal said. “Our staff did a great job. We’ve got some of the best doctors in the world. Our training staff is A-plus. They did a great job getting me ready to go see Tim.”

Tim is Tim Grover. He’s better known as Michael Jordan’s former trainer who earned his reputation by punishing his charges with no-nonsense workouts. You don’t go to see Grover for a magic remedy. You see Grover to work.  O’Neal paid for that trip out of his own pocket and spent three weeks getting himself ready and trying to remove all doubt.

The first week was about establishing a baseline. The second was trying to maintain that level, and the third? “The third week was about how much can I take,” O’Neal said. “I was going twice a day, some of the most challenging workouts … after 15 years [in the league], that was at a different level.”

There were no expectations when O’Neal returned to the team. Literally, coach Doc Rivers said he had none. There were no breathless round the clock updates on his condition, the way there have been for the other half of the O’Neal brothers as Rivers likes to call them.

But there was Jermaine O’Neal, jumping center for the Celtics in their first playoff game against the Knicks. It was strangely fitting in a way because that’s the way the team envisioned it when they signed him in the summer for the full mid-level exception.

O’Neal took six shots and made all of them. He grabbed four rebounds, blocked four more, altered a few others and took a charge from Amar’e Stoudemire that swung the game completely around. He did all that in 22 minutes, which is 22 more than most people had in the pool when he underwent that surgery.

“We won the game tonight because of Jermaine O’Neal,” Rivers said. “That’s it. I mean he was – forget his offense. His defense, his presence, his shot-blocking, his rebounding, his toughness – and he did it in both halves. He was absolutely wonderful.”

No, things didn’t work out the way they had planned last summer. Jermaine O’Neal was supposed to play 50-60 games and if they could get 50 or so out of Shaq then the O’Neal brothers would combine to form a functional center. Like Voltron, but with less meniscus cartilage. Instead the O’Neal’s played 63 games between the two of them and left the Celtics in a terrible state of affairs for a good chunk of the season. None of that matters now because Jermaine O’Neal helped win a playoff game for the Celtics. 

“The big thing with him is he’s healthy,” Kevin Garnett said. “His body feels good. He’s playing well. He has confidence in his body and what he’s doing. We’re feeling him. We’re looking for him. He’s a threat in our offense. I’m happy for him, man. I know he’s grinding and he’s been going through some difficult times with his leg and his body, so it’s good to see him out there.” 

The interesting thing Sunday night is when O’Neal was out there. For most of the season, Rivers has used Glen Davis with his other four starters down the stretch. That lineup has logged more minutes than any other combination he has tried. They know each other and that familiarity is one of the hallmarks of the way they play.

As usual, that was the group on the floor with a little less than six minutes remaining and the Celtics down by two points. That was also when Rivers called an audible.

“That’s not how I planned it,” Rivers said. “J.O. was playing so well and we needed stops. I felt that because of our stops we could get offense. So that was gut. But with the way J.O. was playing, it wasn’t that hard a decision to make.”

There are many reasons why Rivers has excelled as a postseason coach. His playcalls out of timeouts remain a work of art, as they were Sunday night. But it’s his feel for the game and his willingness to make difficult decisions that separates him from his peers. Sure, the way O’Neal was playing made it easier, but he still had to make the call to go away from the one lineup he absolutely knows works in those situations.

Unfortunately, it didn’t work. Not right away at least. O’Neal picked up two quick fouls, including an illegal screen, and the Knicks quickly built a five-point lead. But Rivers stayed with it and that’s when O’Neal took a charge.

By way of build-up, Stoudemire had just dunked over everyone in the building and now he was flying down the lane again about to put someone else on a poster. As he has done throughout his decade and a half in the league, O’Neal rotated over and took it.

“That’s what he does,” Rajon Rondo said. “He takes charges. He blocks shots. That’s what he’s been doing his whole career. There’s a big reason why we wanted to get him, [it’s] because of his defensive energy.”

O’Neal was just getting started. The next time down he blocked a shot and then buried a short jumper in transition to tie the game. The Celtics went on to win – barely – because Rivers drew up two fantastic plays and the players executed them the way they used to do so automatically earlier in the season. But without those defensive plays from Jermaine O’Neal, none of that happens.

Before the game, Knicks coach Mike D’Antoni noted that in the fourth quarter his team couldn’t get stuck playing the Celtics game. “If we try to play like they play,” D’Antoni said. “We could be in trouble.”

But how do the Celtics play? Everyone in the league knows what they do and how they do it, but it’s been a while since it actually went down that way and everyone also thinks they know why. 

There are a lot of conclusions to difficult problems that have taken months to unravel that can be swayed by the force of one phenomenal performance this time of the year. So … Kendrick Perkins.

“I don’t know, I think our team was fine,” Rivers said. “But outside it’s going to keep getting talked about. Perk will probably have a 20 and 20 tonight and it’ll start all over again. And I actually hope it does. It would be great for him. At the end of the day, this is who we are. This is who we have.”

They have Jermaine O’Neal and for one night he was everything they hoped for and everything they needed.