MIAMI - The Miami Heat beat the San Antonio Spurs 103-100 after overtime on Tuesday to square the series at 3-3 and force the NBA Finals to a decisive Game 7.

Miami's LeBron James shrugged off a poor start to get 32 points, 11 assists and 10 rebounds while Ray Allen hit a 3-pointer with 5.2 seconds to play to force overtime.

James scored 16 points in the fourth quarter to rally the Heat from a 10-point deficit. He hit a 3 with 20 seconds to go and Allen drilled another to tie it.

James' layup with 1:43 to play in overtime gave the Heat a 101-100 lead, and Allen added two free throws to force Game 7, which is on Thursday night in Miami.

"If we were going to go down tonight, we're going to go down with me leaving every little bit of energy that I had on the floor," James said.

The Spurs had one final chance when they were down 103-100, but Chris Bosh blocked Danny Green's 3-point attempt from the corner as time expired.

Tim Duncan scored 30 points for the Spurs, his most in an NBA Finals game since Game 1 in 2003, but was shut out after the third quarter. He added 17 rebounds.

Thursday's decider will be the first Game 7 to be played in an NBA Finals since the Los Angeles Lakers beat the Boston Celtics in 2010.

"They're the best two words in sports: Game 7," Heat coach Erik Spoelstra said.

The Spurs looked headed to a fifth title in five chances when they built a 13-point lead with under 4 minutes left in the third quarter, then again when they recovered from blowing that lead to take a five-point edge late in regulation.

Miami, which hasn't lost consecutive games since Jan 8 and 10, is trying to become the fourth team to win the final two games at home since the NBA went to the 2-3-2 format for the finals in 1985.

James came in averaging 31.5 points in elimination games, highest in NBA history, according to a stat provided through the NBA by the Elias Sports Bureau.

He was well off that form early, sinking just 3 of 12 shots over the first three quarters. With the Heat trailing by 10, frustration was apparent among the players and panic was setting in among the fans.

However he finished 11 of 26, even making a steal after his basket had given Miami a lead in OT.

This wasn't quite the 45-point performance in Game 6 of last year's Eastern Conference finals in Boston, but given the higher stakes may go down as more important - if the Heat follow it with another victory Thursday.

The Heat were in the same place as they were in 2011 at the end of their Big Three's first season together, coming home from Dallas facing a 3-2 deficit in the finals and on that occasion they couldn't rally.

This time they said they welcomed the challenge and the chance to show they how much mentally tougher they were than the team the Mavericks easily handled in Game 6 that year.

Kawhi Leonard had 22 points and 11 rebounds for the Spurs. Tony Parker had 19 points and eight assists, but shot just 6 of 23 from the field.

When the ball came to Green at 3-point range for the final shot, Miami fans had their hearts in their mouths - Green had shot 25 of 38 (65.8 percent) from beyond the arc over the first five games of the series.

Bosh had vowed Green would not be given as much as space as he had in the previous five games and proved true to his word by producing the game-saving block, leaving Green with a 1-from-5 performance on 3-pointers.

The Heat, the NBA's 66-win powerhouse during the regular season, will be playing a seventh game for the second straight round, having needed to go the distance to beat the Indiana Pacers in the Eastern Conference finals.

The Heat are 13-0 after losses over the last five months, though this was nothing like the previous 12 that had come by an average of nearly 20 points. Nor was it like the previous four games of this series, which had all been blowouts after the Spurs pulled out a four-point victory in Game 1.

San Antonio had an 11-0 run in the first half, then a 13-3 burst in the third quarter for a 71-58 lead, and a final flurry late in regulation that seemed to have them ready to walk off with another title.

Parker's 3-pointer over James tied it at 89 with 1:27 left. He then came up with a steal, spinning into the lane for a 91-89 lead with 58 seconds to go. Miami coughed it up again and Manu Ginobili made two free throws, and he made another after a third straight Miami turnover to put the Spurs ahead 94-89.

James nailed a 3-pointer with 20 seconds left, and the Heat had one more chance after Leonard made just one to give the Spurs a 95-92 edge. James missed but Bosh got the rebound out to Allen, the league's career leader in 3-pointers, who made another one from the corner to even it up.

The Spurs went ahead by three again in overtime, but James found a cutting Allen for a basket, then scored himself to put the Heat on top. They clinched it when Bosh blocked San Antonio's final two shot attempts.

Bosh finished with 10 points and 11 rebounds.

NBA Finals

Game 1: Spurs rallies to beat Heat in opener

Game 2: Heat beat Spurs to level series

Game 3: Spurs routs Heat  113-77 in Game 3

Game 4: Big 3 help Heat even with Spurs

Game 5: Ginobili sparks Spurs to Game 5 win