J.R. Smith is ejected from the game after fouling Boston...

J.R. Smith is ejected from the game after fouling Boston Celtics' Jason Terry during the fourth quarter of Game 3 of the Eastern Conference quarterfinals. (April 28, 2013) Credit: AP

The Knicks will have at least three days now to ponder how different their week might have been if only they had had one more big basket, or if Carmelo Anthony had not felt compelled to shoot quite so early and often.

For that they can thank J.R. Smith, whose absence yesterday because of a one-game suspension could well have cost them a first-round sweep of the Celtics, several days off from practice and an entire week before their next game.

Instead, they fell in overtime, 97-90, in Game 4 at TD Garden and now must go back to work Wednesday night at their own Garden, hoping to close out the Celtics without anyone getting hurt.

The winning part should not be a problem; the Knicks still are the better team, and Sunday's hiccup should not affect the bigger picture of their playoff run.

It did, however, illustrate the importance of keeping Smith's head straight moving forward.

One seemingly intentional elbow to Jason Terry's chops should not erase all of the good will he built up on and off the floor en route to being named the NBA's Sixth Man of the Year. He has earned that.

But the Knicks cannot afford anything other than spotless behavior from him moving forward, because without him, they are extremely vulnerable on offense, especially when Anthony is not on his game.

Don't take my word for it. Here is Raymond Felton, who said he did what he could to compensate -- and looked great doing it during a 16-point third quarter that helped the Knicks erase a 20-point deficit:

"You've got a guy who's the second-leading scorer on the team, averaging over 18 points a game. He's a guy who hits tough, big shots for us down the stretch. We definitely missed J.R. offensively, for sure."

What about Anthony, who scored 36 points thanks mostly to going 16-for-20 from the line but was off-target from the floor, shooting 10-for-35 (0-for-7 on three-pointers)?

He said he learned of Smith's suspension late Saturday night and "of course it put a damper into a lot of our plans. We were looking forward to having him in this game, but we didn't."

Still, although Anthony admitted he missed Smith, he said Smith's absence didn't cause him to miss so many shots, nor did it cause him to be overly anxious to carry the offense.

"I was trying to win a basketball game," he said. "I was just trying to be aggressive."

Knicks coach Mike Woodson shied from using Smith's absence as an excuse, but Celtics coach Doc Rivers noted the obvious when he said, "You just don't know what the impact was, but guarding one less guy can't hurt."

The entire episode was a shame, given how far Smith has come, and a reminder that reputations are delicate things.

At halftime, ESPN/ABC analyst Magic Johnson did not hold back, saying, "I'm disappointed in J.R. Smith . . . You have a chance to get a big contract. You've just been named Sixth Man of the Year. Your reputation with the Knicks has really helped you, then you throw an elbow that cost you. And now you're suspended for this game, a game that the Knicks could have swept the Celtics."

Adding to the insult for the Knicks was the fact that Terry scored his team's final nine points in OT as the Celtics broke away from a tie at 88. "Maybe that elbow, who knows, changed the events for all of us," said Rivers, who added that Terry had been angry about it and told his teammates so.

It is wishful thinking on Rivers' part that Smith's suspension and Terry's response could change the course of the series, beyond extending it longer than should have been necessary.

But the incident should be another lesson for Smith: He has no margin for error in the eye of the public, the officials and the NBA. Everyone will be watching him more closely than ever -- and the Knicks need him now more than ever.