NEW YORK -- Before the Mavericks game on Sunday, Mike D'Antoni told the Knicks' newest acquisition, J.R. Smith, that he was barely going to play. And if he did, expect limited minutes.

But soon after Iman Shumpert was subbed out, picking up two quick fouls within seconds apart about nine minutes remaining in the first quarter, D'Antoni realized he needed perimeter play, especially 3-point shooting. He couldn't turn to Bill Walker, who had been starting in place of the injured Carmelo Anthony, because he was out of action with a sore left elbow.

At that point, D'Antoni signaled to Smith to enter the game with 5:43 left in the first period -- after just one day in New York, with no practices under his belt.

"Coach really shocked me," Smith said. "He told me I was barely going to play. If I did get in the game, it would probably be in limited minutes. I was in a great situation, going down the stretch and having that confidence in me. My teammates were unbelievable. They really helped me out big time. With that confidence right there, that's all I needed."

D'Antoni had nothing to lose and everything to gain playing Smith. Entering Sunday, the Knicks were second-worst in 3-point accuracy (29.9 percent), a far difference from last season when the Knicks were eighth-best at 36.8. Smith is dead-on from downtown with a career 37.1 percentage. In fact, in the past five NBA seasons, he's made 771 3-pointers (including Sunday), which ranks him fifth on the list that includes the Celtics' Ray Allen.

When Smith came into the game in the first quarter, he made an immediate impact on the defensive end with a steal on Mavericks point guard Jason Kidd, which led to a Jeremy Lin fastbreak layup. Then, Smith got going from his favorite place on the court. Within five minutes, he hit three 3-pointers and helped lead the Knicks to a 32-20 first-quarter advantage. The 32 points was the third-highest Dallas have given up all season.

Smith said he was worried about being out of rhythm when he checked in, but he said Lin was helpful in providing him some much-needed confidence. The Knicks' point guard told him not to worry about shooting the ball.

"The first five minutes were really mind-blowing," Smith said. "The whole time during warmups I was just saying, 'This is crazy.' I'm at the Garden.' I never imagined this in a million years, and to be out there for that first five minutes, the first thing I was thinking was, 'Don't air ball your first shot.' Once I made the first one, that really got me going.

"Jeremy was telling me, 'Every time you play this game, don't do anything different. This is how we wanted you and this is why you're here and keep playing your game and we don't mind if you shoot the ball.' And that's what I did. That really helped me."

While Smith shot 6-for-16 for the game off the bench (he had 15 points in 30 minutes), he made an immediate impact on his teammates. Steve Novak talked about it in the postgame locker room.

"He was huge," Novak said. "Everybody had their thoughts about what J.R. Smith would bring to the Knicks, and how he was going to play for us. I feel like he lived up to it. You see he wasn't forcing. He was able to spread the floor, he was able to knock down big shots. And I think when we're making shots, it just makes everybody's job easier, and that's what he does."

When Smith addressed reporters after the game -- in the extended press room seating area made up for Linsanity -- he confirmed his free agency decision came down to the Knicks and Clippers. While Smith said he and Chris Paul are very close -- in fact, Paul is a godfather to his two small children -- three main factors helped him seal the deal to sign with the Knicks: Carmelo Anthony, a return home (he's from New Jersey) and the opportunity to play within D'Antoni's spread-out, perimeter-based offense.

Smith said Anthony, his former Nuggets teammate, made him excited about the Garden atmosphere when they talked on the phone a couple of times. He also knew his family and friends, like Sunday afternoon, would be able to watch him live. What he saw playing for D'Antoni was an opportunity to incorporate his exact game.

"This offense matches my game to the T," Smith said. "Fast-paced, run the lanes, get open and shoot the ball. Now, it's more defensively. The pieces for this team with Tyson, Amare and Melo, those guys are really defensive-oriented. That really helped me out to build confidence to go out and play against Dirk [Nowitzki] and those guys. To see how positive everybody is around the building, it really helped me out. It was really a no-brainer. It was a perfect situation for me. I would've been a fool not to take it."

Smith said his experience playing in China during the lockout, one he would duplicate "in a heartbeat," helped him mature as a player and person. Some have questioned Smith's checkered past, including his involvement in a major brawl at the Garden on Dec. 16 2006, as a member of the Nuggets. But he's ready to prove the critics wrong.

"It's definitely a clean slate," Smith said. "I'm just really getting to know the coaches, getting to know the system, getting to know the people around the arena. I'm not the same 18-year-old kid that I was eight years ago. I mean, I'm a grown-man, 26 years old and ready to make big decisions for my life and make the best decisions for my teammates."

The Knicks know he's already made a big decision by signing with them. And based on his performance on Sunday, things can only go up for him and the Knicks, who are becoming one of the deeper teams in the league and a dangerous one come playoff time.

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