BOSTON (AP) -- Carmelo Anthony scored 21 points and the New York Knicks held on after blowing most of a 26-point lead to beat the Boston Celtics 88-80 in Game 6 on Friday night and advance in the postseason for the first time since 2000.
Iman Shumpert scored 15 of his 17 points in the second half, when the Celtics cut a 75-49 deficit to four points. But Anthony made a jumper to give New York an 81-75 lead and followed with a 3-pointer, then J.R. Smith converted a three-point play to restore the double-digit lead the Knicks had nursed most of the game.
The Knicks will open the Eastern Conference semifinals against the Indiana Pacers in New York on Sunday.
Jeff Green scored 21 points for the Celtics, who had rallied from a 3-0 deficit in the series and had a chance, at home, to force a decisive seventh game.
No NBA team has advanced in the playoffs after losing the first three games.
Paul Pierce scored 14 points on 4-for-18 shooting, making one of nine 3-point attempts. Anthony also struggled from in- and outside the arc, going 7 for 23 from the floor and missing his first five 3-point attempts -- that was 19 in a row in the series -- before sinking the key basket with 1:43 to go.
The Knicks had not won a playoff series since Patrick Ewing and Latrell Sprewell (and current backup center Marcus Camby) helped them reach the 2000 Eastern Conference finals.
Kevin Garnett had 15 points and 10 rebounds for the Celtics, who now face another offseason of talk whether to break up the aging core that won the franchise's record 17th NBA title in 2008 and returned to the finals two years later. Reserve Jason Terry scored 14 points -- the only points the Celtics got from their bench.
After winning the first three games of the best-of-seven series, the Knicks lost two straight. A win on Friday would have made the Celtics the fourth NBA team to tie a series after losing the first three games. And it would have given them a chance to be the first in league history to win a series after trailing 3-0.
The Celtics called upon local history to rally them, playing highlights on the scoreboard from the Red Sox comeback against the New York Yankees after a 3-0 deficit in the 2004 AL championship series.
But Boston quickly fell behind 21-5 and trailed by double digits most of the way. The Knicks made it 75-49 with just under 10 minutes left before the Celtics scored the next 20 points, holding New York scoreless for 4:43 before Pierce threw the ball away and Shumpert took it in for an easy layup that made it 77-69 with 5 minutes left.
Avery Bradley made a layup, then Green hit a pair of free throws to make it a four-point game. It was 79-75 when Anthony made a 13-footer and then followed Pierce's missed 3-pointer with a 3 from the top of the key. He then stripped Pierce going to the basket, and Smith converted a three-point play at the other end -- Green fouled out on the play -- to make it 87-75.
Notes: Lines of fans were still waiting to get through the increased security at 7:20, about 10 minutes after the game started. ... Garnett's six points in the first quarter were twice as much as the rest of Boston's players combined as the Knicks took a 24-10 lead into the second quarter. ... The Celtics were 4 for 16 from the floor in the first and missed all six of their 3-point attempts. The Knicks also outrebounded Boston 13-7 in the period. ... Boston shot 23.5 percent in the first half. ... The Knicks made 5 of 6 3-pointers in the third quarter.