Smith received 484 points, including 72 first-place votes, from a panel of 121 writers and broadcasters. The Clippers' Jamal Crawford finished second with 352 points, getting 31 first-place votes.
Smith averaged 18.1 points in 80 games, all off the bench. He had 29 games in which he scored 20 points as a reserve, tying Crawford for the NBA lead.
The 6-foot-6 swingman wanted to start, but said he accepted it fairly quickly once coach Mike Woodson told him he would be a reserve.
The New Jersey native had by far his best NBA season, helping the Knicks to their first Atlantic Division title since 1994.
"I just wanted to show everybody that I could be a team guy and it's all about the team," Smith said at a news conference attended by his family, teammates and coaches.
Smith helped the Knicks to their most victories since they went 57-25 in 1996-97. New York is the No. 2 seed in the Eastern Conference and leads the Boston Celtics 1-0 in their first-round playoff series.
It's the second individual award in two years for the Knicks, following Tyson Chandler's Defensive Player of the Year honor last season. Smith joins former Knicks sixth-man winners Anthony Mason in 1995 and John Starks in 1997.
Despite not making a start, Smith was one of the Knicks' most important players. He played more than 40 minutes seven times and was often their only scoring threat behind Carmelo Anthony.
"Couldn't have happened to a better guy," Woodson said. "I'm so proud of him, in terms of buying into what we wanted him to do earlier in the season. And it started this summer. I wasn't going to start him, coming into this year, and I knew that. And he bought in. He didn't like it, but he bought in. And it couldn't have happened to a better person, because he put in the time and he worked his butt off to get to this point, and he got rewarded for it. I'm happy for him."
Crawford seemed to be the favorite for most of the season before Smith overtook him with his strong play down the stretch. He had three straight 30-point games from March 26-29, the first time that was done by a reserve since Milwaukee's Ricky Pierce in 1990.
"I more credit it to winning," Smith said. "We've had guys hurt, it just so happened I was one of the guys that stepped up and tried to get us through the tough times that we had."
Golden State's Jarrett Jack finished third, followed by Kevin Martin of Oklahoma City and Ryan Anderson of New Orleans.
Smith joined the Knicks in the middle of last season after returning from China, where he had signed during the lockout. But it wasn't until the middle of this season when he finally learned to stop settling for erratic jumpers, instead taking smart shots.
"The opportunity was there," said Anthony, a former teammate in Denver.
"They asked me what I thought about him, I told them we'll be fools not to go get him. At that point in time he was the only thing that was out there, he was trying to get out of China, and we had to go get him. I'd played with him for mostly all my career so I know what type of person he is, I know what type of player he is. And this right here was almost like a second chance for him."
Smith came to the NBA out of high school in 2005 and admittedly made a number of mistakes along the way. He clashed with coaches and pleaded guilty to reckless driving in a 2007 auto accident that killed his friend, spending 24 days in a New Jersey correctional facility and getting suspended by the NBA for the first seven games of the 2009-10 season.
"I've been to known to make so many mistakes I haven't been making recently," said Smith, thanking his veteran teammates and Woodson for helping him. "Just keeping my head, mentally on the court and off the court."
Teammate Kenyon Martin said the 27-year-olf Smith has "grown up a lot."
"I played with him a lot of years in Denver, he was still a kid then. He's become a grown man," Martin said. "I think he's got better people around him, which is huge, and he's learning. He's learning on the fly, that's all you can do is keep learning each and every year you're in the league."
The award is sponsored by Kia Motors, which will donate a 2014 Kia Sorento to the J.R. Smith Youth Foundation.
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