Before Kendrick Perkins’ emotional return to Boston, the Celtics had played 38 regular season games. They had won 19 and lost 19 with a disappointing second-round loss to Miami in between.

The Perkins trade has become a flashpoint in Celtics history, the moment when they morphed from the toughest dudes on the block to a finesse team with no inside presence. You can’t convince anyone that this is not the whole truth any more than you justify the deal that left the Celtics with 50 games from Nenad Krstic and Jeff Green, a far-off draft pick that is coming from a much-improved Clippers team and a nebulous concept like cap space.

So, it was somewhat fitting that on a night when Perkins and the Thunder gave the Celtics a losing record since the trade with a 97-88 victory, and established the first five-game losing streak in the Big Three era, that the beloved big man was outplayed by Jermaine O’Neal who outscored him, 12-7, and outrebounded him, 11-5.

The Celtics lost because they turned the ball over 19 times, which yielded 24 points to the Thunder and because Oklahoma City dropped five straight 3-pointers after missing 12 of their first 14 from behind the arc. The game had little to do with Perkins, but his long shadow continues to cast a pall over this team.

“They’re going to be good,” Perkins said earlier on Monday after Oklahoma City’s shootaround. “They’re going to make the playoffs and whatever team they got to face I feel sorry for that team because you’ll see it. I think they’ll hit their stride by late February into April. You’ll see them run off about 10, 11 games in a row and sneak into the seventh, sixth spot and make some noise in the playoffs. That’s what I believe.”

Deep down, the Celtics believe it too. They felt better about themselves after outrebounding the Thunder and especially after Paul Pierce went for 24 points and genuinely looked like Paul Pierce while he was doing it. Doc Rivers felt good about O’Neal, Kevin Garnett’s 19 shots (although not his five makes), Mikael Pietrus’ energy and toughness and even E’Twaun Moore’s ability to handle Oklahoma City’s pressure.

“It’s nothing positive about losing, that’s first,” Garnett said. “But we’re trying to make progress. When you’re trying to make progress you have to pull the pluses out of everything and I think we’re making progress.”

That’s the (sort of) optimistic view about their latest defeat. The cold-eyed cynic notes that this was the best game the Celtics have played this season and they still lost by nine points at home. The turnovers have been a staple of this team since it was created in 2007, but they usually found a way to play through them. They still can’t find enough offense and have to resort to calling timeouts to run plays to get them through tough times.

“I don’t want to be playbook team,” Rivers said. “Right now it seems like to score we have to call a timeout and draw something up. We can’t win that way.”

The Celtics will get better. Pierce will continue to work his way back into shape, the bench will settle down and there will be nights when more than two of the four All-Stars have a good game. The question is, how much better? If the defense, which ranks from mediocre to worse across the board in several key categories, doesn’t improve then the answer is not good enough.

Perkins wasn’t the best defensive player on the team (that was Garnett). He wasn’t the second-best (that would be Rajon Rondo) or even the third (Pierce), but he was a key cog on some of the best defensive teams of the recent NBA era. 

He’s helping the Thunder get there now by playing the same role and doing the same things. Just like in Boston, he’s not the first, second or even the third best player, but he took what he learned from Garnett and brought it with him to Oklahoma. 

“His influence on that team is dramatic to me,” Rivers said. “Perk has completely changed the culture of the team.”

When it was suggested to Rivers that it sounded a lot like Garnett’s influence, the coach said knowingly, “He used Kevin’s playbook.” 

Perk is all grown up, a 27-year old man who transformed his body in the offseason to take pressure off his knees. The Thunder trainers gave him a workout plan and Perkins told them, “I won’t disappoint you.” He sees himself as a big brother, which is how his teammates view him too and he knows that the best way to show leadership is by setting an example. He still regularly talks to Garnett seeking leadership advice. 

“He wasn’t trying to come in here to boss everybody around, or just be that guy,” Kevin Durant said. “He kind of fell into that role, he didn’t force his way into it. That’s the best thing about Perk. He’s all about team first. He doesn’t want anybody to be bigger than anybody else. He came in with the mindset that he wanted to learn with us and get better with us. That’s what makes him so unique.”

The Celtics know that too and if they had to do it all over again, knowing what they know about what happened to Krstic and Green and that Shaq was never going to come back last season and that the Clippers would get Chris Paul … Or maybe they still would considering the only way out their time warp is the almost $30 million in cap space they’ll have to work with after this season.

In the here and now, the Perkins trade failed to prolong this era. Time will tell if it ultimately helps unlock a new one.