Doc Rivers called it earlier this week. Yes, the Celtics were winning games, and they were playing well, but they had not yet established that defensive identity that has been their trademark the last few years.

That manifested itself in all kinds of ways Friday night in an 89-84 loss to the Oklahoma City Thunder, who were playing without Kevin Durant and Jeff Green. (Click here for a full recap).

“No, it’s not typical Celtics basketball,” said Kevin Garnett who took an elbow to the back of the head minutes into the game and missed the rest of the first quarter. “I just got a ‘bow man,” he said. “And a hell of a ‘bow at that.”

The defense found itself late in the game but by then it was too late. The Thunder shot 57 percent in the first half, made 13 of 16 free throws in the third quarter and when Royal Ivey is banking in 3’s, well, you can curse the basketball gods all you want (and the Celtics did) but they really only have themselves to blame for this loss.

“I asked them to explain how they could hold them to 12 points in the fourth quarter, but for the first three you couldn’t guard them,” Rivers said. “And then all of a sudden you have a sense or urgency and then defensively we were terrific.” 

They had no flow at the outset and then things started snowballing and the Celtics were fighting themselves as much as they were fighting the Thunder. They missed free throws and open shots and couldn’t get to loose-ball rebounds that didn’t bounce their way.

“We just didn’t start the game with the right mindset,” Paul Pierce said.

“I think we underestimated that team,” Shaquille O’Neal said.

“It was just difficult,” Rajon Rondo said. “We shot the ball extremely well. We shot 56 percent in the first half and you’d expect us to be up. We didn’t play well defensively. There were a lot of dare shots. Give them credit. They made shots.”

Nights like this happen in the NBA. Sometimes they are merely bumps in an otherwise smooth road. Sometimes they are the tipping point to something else. There’s no reason to believe that this was anything more than just a bad night at the office, but the Celtics are by no means a finished product.

They have been good defensively, but they have rarely been great for 48 minutes. They have steamrolled teams with their precision offense, but when things didn’t go well on that end they couldn’t come up with the right answers on the defensive end.

That’s a long-term issue for them to address, but by far the biggest concern right now is the health of Rondo, who left the game late in the fourth quarter and had to come back out after a brief return.

That’s where we’ll start:

RONDO HAS A STRAINED LEFT HAMSTRING

It happened when Rondo collided with Ivey who may have done far more damage to the Celtics than his two 3-pointers. Rondo hobbled off the court, tried to return and then was pulled by Rivers after he had obvious trouble moving. The prognosis is a strained hamstring, which is different than the foot problems that plagued him early in the season.

“I’ll get treatment tomorrow and we’ll see,” Rondo said. 

Could he have played through it? “No,” he said. “Doc made the decision. He [saw] me moving, he just decided to pull me.”

Hamstrings are tricky things, particularly for a player who relies so much on his speed and quickness. If Rondo can’t play then the Celtics have an obvious problem.

“Clearly you want Rondo on the floor all of the time because offensively it’s tough to run your stuff when your guy who knows the whole system is not on the floor,” Rivers said.

It was telling that when Rondo had to leave, Rivers turned to Delonte West instead of Nate Robinson who simply hasn’t earned that kind of trust yet. West has only been active for two games but he has already cemented himself as the third guard in the team’s rotation and would likely get the call if Rondo has to miss any time.

“I thought he was a great pickup for us when we got him,” Rondo said. “He doesn’t turn the ball over. He’s very smart. He plays with a lot of tenacity, a lot of energy. He’s a great fit for us.”

West has been everything as advertised on the court. He may have to be even more now.

SCORE ONE FOR WESTBROOK

The Celtics knew, just like everyone else in the building knew, that with Durant and Green out of the lineup, Russell Westbrook was going to have to carry the Thunder. That didn’t mean they could stop the third-year guard who is emerging as a star player in his own right.

“It’s tough when you got Durant on your team but he’s one of the better point guards in the league,” Rivers said before the game. “There’s an elite group of points guards, it’s growing which is really good for our league, and he’s in it. His speed and strength combination is as good any point guard in the league.”

Westbrook scored 31 points, and he did most of his damage in the first three quarters when the Thunder were building their lead. The Celtics made him work, he shot 9-for-21, but Westbrook was a star Friday night and he did what star players do.

“Tonight he got the better of the matchup,” Rondo said. “He played extremely well. He led his team to victory.”

Thunder coach Scott Brooks wanted no part of declaring victory for his guy, which is definitely smart. Rondo is on the level where Westbrook, Derrick Rose and the other young point guards are trying to attain and it’s one of the more enjoyable subplots of this Celtics season to watch Rondo take on all the up-and-comers.

“I thought Russell did a good job, doing the best he can to control him, and I thought [Westbrook] had a good game,” Brooks said. “He got a little crazy in the fourth quarter, taking a couple wild shots. But we will watch film and learn from it and move on.”

Put this one in Westbrook’s column, just like Rondo earned the decisive edge in their matchup two weeks ago. It’s just a shame that we’ll probably have to wait until next season for it to continue.

‘A THIN SHEET OF ICE’

That’s how Rivers described his center situation before the game. There is no further update on Jermaine O’Neal since he returned to Boston a week ago after missing the Heat game.

Shaq had a decent game, scoring 10 points, all in the first quarter, but when Garnett took that shot to the back of his head it was like Rivers’ worst nightmare come to life.

“I’ve felt the last three or four games like you’re playing on this thin sheet of ice,” Rivers said. “There may be a game where we have no centers and that may be soon.”

With Garnett out, Rivers rode Shaq as long as he could, playing him almost 11 minutes in the first quarter. But the big fella has only so many minutes left in his body and he was noticeably less effective the rest of the game.

That’s why it’s important for them to win as many games as they can right now, and take advantage of their opportunities when they present themselves. “If we had won the game I would’ve been happy with the win, but known that we didn’t deserve the win,” Rivers said. “So we didn’t.”