Rondo’s 20-point, 6-assist, 2-steal performance is forgotten because he was unable to convert the last-second freebies, which, along with perimeter shooting, is his biggest weakness.

Rondo appeared unfazed after the Celtics’ 92-90 loss, but not only did he miss the free throws with the score 90-90, his counterpart, Baron Davis, drained a 22-foot, buzzer-beating shot with Rondo looking on helplessly.

Rondo’s success at the line has been an issue most of the season, but, entering last night’s game at Golden State, he improved to 60 percent in December after shooting 38 percent in November. Yet, even after a 7-of-9 showing in a 103-99 loss to the Warriors last night, he’s last on the team at 55.4 percent.

Earlier in Sunday’s game, he hit two of three free throws. But they didn’t come with the pressure of those final two attempts, with a sellout crowd at Staples Center jeering him.

While Rondo is a candidate to make the All-Star team, he still needs to prove to teammates - and perhaps himself - that he can deliver in the clutch. Sunday, he failed his first mid-term exam.

“I felt confident shooting them,’’ he said. “The first one was long and the second one was long. I kept my follow-through up, I think. I was breathing, took my time - I just missed it.’’

His veteran teammates are hoping it will serve as motivation.

“I told him after the game that we have all been in that position,’’ Kevin Garnett said. “We’ve all made them. We’ve all missed them, and I have the confidence in him to go up and make those. If he is to go up there 100 times, I am going to support him 100 times, if not 101.’’

Rondo’s free throw shooting has slightly improved since he changed his release before the victory over the Knicks Nov. 22, but he is 12 for 21 the past three games and the more he improves offensively, the more he is going to get fouled.

“I’ve missed plenty of free throws [with the chance] to win games,’’ said guard Ray Allen, who is second in the NBA at 90.4 percent from the line, “so now when I get to the free throw line, you remember those moments and you can put that moment right there on you when you’re practicing.’’

Perkins had a tough night checking Los Angeles’s Chris Kaman, and that led to frustration, two crucial fourth-quarter fouls, and an on-court exchange with Garnett.

Perkins, who scored 9 points and had 6 rebounds in 26 minutes, admitted he was “not himself.’’

“I think a few little things took me out of the game,’’ he said. “Obviously I was frustrated the whole game - I just feel like I have to do a better job of holding my composure. A couple of fouls down the stretch, stupid fouls that I made, was probably the difference in the game, so I’ve just got to do a better job of staying focused.’’

With 1:41 left in the game, Garnett gave Perkins some stern advice about how to defend Kaman and remain focused.

Perkins barked back at Garnett, a testament to the Celtics’ frustration in the final quarter.

“It was a lot of other things that probably shouldn’t have even bothered me that I’d rather not say,’’ Perkins said. “It was just something that I have to do a better job of holding my composure. It ain’t nothing that can’t be fixed.’’

Perkins said the exchange with Garnett was just a culmination of his anger.

“One thing triggered another and another thing triggered another,’’ he said. “Like I said, it was just a frustrating day. The good thing is we got another day to redeem myself.

“I felt like we were going to walk into the game and just win that one, just showing up . . . you tend to look at team’s record and think that’s how it’s going to be and it’s not.’’