GREENBURGH, N.Y. – J.R. Smith may have altered a series with one poor decision. He certainly forced his midweek plans to change.

When he dropped Jason Terry of Boston with an elbow to the chin Friday night late in Game 3, Smith earned a suspension that left the New York Knicks without their No. 2 regular-season scorer for Game 4 on Sunday.

The Knicks didn’t have enough offense without him, losing 97-90 in overtime as Terry hit the big shots off the bench. Had Smith been available, perhaps this series would be over.

“It would have been,” Smith said Tuesday. “I would have been playing golf today.”

Instead he was practicing for Game 5.

The Knicks will be at home Wednesday, their second attempt to close out their first series victory since 2000.

“We want to end it,” Carmelo Anthony said. “We came this far, did our job at home the first two games, did our job on the road, got one on the road. We’ve got the opportunity to end it here on our home court.”

The Knicks won the first three games, holding the Celtics to an average of 75 points before Boston broke out — sort of — on Sunday. The Celtics scored 54 points in the first half and led by 20 early in the third quarter before their struggles returned. They were limited to 30 points in the third and fourth quarters.

Clean up those bad stretches and the Celtics think they can keep climbing out of the mess they created for themselves.

“There’s that one quarter where we have mental lapses,” forward Paul Pierce said. “They pick up the energy. They pick up the defense and they have us on our heels, so we have to be cautious of that.”

The Knick had their own problems Sunday, shooting 34 percent and making 7 of 30 3-pointers (23 percent). Anthony scored 36 points but was 10 of 35, missed all seven 3-pointers and committed seven turnovers.

Smith averaged a career-best 18.1 points in the regular season, and his recognition as the NBA’s top reserve was as much a credit to his improved maturity and decision-making as it was to his scoring streaks.

But those qualities went missing Friday when Smith threw his elbow into Terry with the Knicks 7:06 away from wrapping up an easy victory. Coach Mike Woodson appeared to be lecturing Smith before he left the court and they had another talk Sunday.

“We had a major discussion before he left Boston to come to New York,” Woodson said. “J.R.’s in a good place. We’re fine with J.R.”

No team has blown a 3-0 lead in the NBA playoffs. The Celtics would send the series back to Boston for a Game 6 on Friday with a victory.

“We have to bring it. It’s the only way we have a chance to win the game. We just have to play all out,” forward Jeff Green said.