NBA

Rivers: Celtics need to step it up

Boston coach Doc Rivers has seen the exact sort of frenzied desperation his Celtics need tomorrow in Game 3 to maintain any realistic hope of staying alive in the Eastern Conference first round playoff series.

Yes, he has seen that display already in the series. The problem is, he has seen it from the Knicks.

“At the end of the day, we cannot be outplayed in the effort department, in the desperation department,” Rivers said Wednesday. “I really thought in the second half of [Game 2], the Knicks played like their season was on the line and I didn’t think we answered it.”

What would make Rivers think his gang didn’t respond? The fact they were outscored 32-11 in the third quarter? Maybe the way they rolled up 23 points in the entire second half? Or maybe the way the Knicks got rolling and simply did not quit?

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So Game 3 Friday is huge for the Celtics to turn this into a series. Lose in Boston, where the Celtics last played April 10 against the Nets, and face the inevitability of an 0-3 deficit, and these Celtics are not the 2004 Red Sox.

The Boston Marathon tragedy forced the cancellation of the Celtics’ final home game, and they have been on the road ever since.

“It’ll be great to be home,” Rivers said. “Obviously this is extreme circumstances. We missed our last home game of the year. I don’t know if that’s ever happened.

“First of all, it’s just good to be back in Boston, period. Second, it will feel great and be great to be back in the [TD] Garden playing in front of our fans. We have to play better. We have to play harder.

“Clearly, the Knicks came out in the second half and acted far more desperate than we did. And it showed in the way they played.”

Rivers also said Kevin Garnett, who had little offensive impact in Game 1, was battling a sore hip pointer — as well as catastrophic foul trouble — in Game 2.

“[It was] very similar to a hip pointer in football,” Rivers said. “It was affecting him. I was concerned that he had done something else where he was grabbing it — you know where you pull a stomach muscle.

“I kept asking him in timeouts if he was OK. He’s good, good to go. He’ll practice [today] and play [tomorrow].”

Rivers also said he is hoping the Celtics can keep Garnett away from foul-inducing matchups and situations. One good starting point would be to limit Knick guards’ penetration, especially by Raymond Felton.

“He’s killing us,” Rivers said. “He’s getting into the paint. He’s attacking us. … We have to keep him out of the paint.”

Despite all of the Celtics’ offensive woes — seven turnovers in the last 5:30 of an eight-point Game 1 fourth quarter, 23 Game 2 second-half points — Rivers knows his guys can execute and perform against the Knicks. He has seen it in first halves. Now, he wants to see that reach down deep desperation stuff — and not only from the Knicks.

fred.kerber@nypost.com