San Antonio Spurs power forward Tim Duncan (21) shoots under pressure from Miami Heat small forward Shane Battier (31) during the first half of Game 6 of the NBA Finals basketball game, Tuesday, June 18, 2013 in Miami. San Antonio Spurs center Boris Diaw (33) of France, blocks a shot to the basket by Miami Heat small forward LeBron James (6) during the first half of Game 6 of the NBA Finals basketball game, Tuesday, June 18, 2013 in Miami. Miami Heat center Chris Bosh (1) and San Antonio Spurs forward Tim Duncan (21) work on the court during the first half of Game 6 of the NBA Finals basketball game, Tuesday, June 18, 2013 in Miami. San Antonio Spurs head coach Gregg Popovich calls a play against the Miami Heat during the first half of Game 6 of the NBA Finals basketball game, Tuesday, June 18, 2013 in Miami. Miami Heat shooting guard Dwyane Wade (3) grimaces after landing badly on his right knee during the first half of Game 6 of the NBA Finals basketball game, Tuesday, June 18, 2013 in Miami. San Antonio Spurs power forward Tim Duncan looks on (AP Photo/Lynne Sladky) MIAMI (AP) - Tim Duncan scored 25 points and grabbed eight rebounds to lift the San Antonio Spurs to a 50-44 halftime lead over the Miami Heat in Game 6 of the NBA Finals on Tuesday night. Duncan made 11 of 13 shots in a performance straight out of 2003 and Kawhi Leonard added 10 points and five boards as the Spurs looked to close out the Heat and win their fifth NBA title. Mario Chalmers broke out of a shooting slump to score 14 points and LeBron James added nine points, five assists and three boards for the Heat, who trailed the best-of-seven series 3-2 and needed to win to keep their hopes of defending their championship alive. Game 7, if necessary, is Thursday night in Miami. Duncan hit his first eight shots of the game, conjuring the dominant form that brought four titles to San Antonio between 1999 and 2007. But he long ago handed the reins of the Spurs offense over to Parker, letting the speedy French point guard take over as Duncan grew older. Until Tuesday night. After getting a vintage performance from Manu Ginobili in Game 5 to take control of the series, the Spurs got a throwback effort from Duncan to start Game 6. With the Heat leading 40-33 and threatening to pull away with 7:30 to go in the first half, Duncan scored San Antonio's next 13 points to start a 17-4 run that closed the half. Chalmers' floater gave the Heat a seven-point lead, and the charged up home crowd sensed that their team was finding that fifth gear that had eluded them so often in this series. That's when Duncan went back to work to keep the Spurs in the game. The old man blew past Chris Bosh for a crafty left-handed layup, scored on a put-back and took Chris Andersen wherever he wanted to during the surge, finishing it off with a dunk that gave the Spurs a 46-44 lead with 1:24 to play in the half. With his championship-winning teammates Parker - four points, six assists - and Manu Ginobili - scoreless on 0-for-2 shooting - quiet, the Spurs have never needed him more. They entered the game with title No. 5 sitting right there in front of them. They had two cracks to bring the trophy back home to San Antonio, but the last thing they wanted was to have to play a Game 7 against LeBron James on the road for the championship. There have only been five Game 7s in the finals since 1978, with the home team winning all those contests. The last road team to win a Game 7 for the title was the Washington Bullets over the Seattle SuperSonics in 1978. Chalmers was 4 for 19 over his last three games, but came alive in this must-win for Miami. He made 5 of 7 shots, including two 3s, to get the Heat out quickly. Chris Bosh added six points and three rebounds Dwyane Wade seemed to tweak his left knee after being whistled for an offensive foul early in the first quarter, but he looked fine moments later when he dunked over Duncan to tie the game at 16. Leonard responded by dunking on Mike Miller on the other end, and a scintilating first half was off and running. After getting a vintage performance from Ginobili in Game 5 to take control of the series, Duncan got them going to start Game 6. The big man threw down a dunk, hit a turnaround jumper and muscled a one-handed hook over Shane Battier - all while patrolling the paint on defense - to give the Spurs a 24-19 lead in the first eight minutes. The Heat appeared stunned once again. It's been 12 games since the Heat have won two in a row, a startling stretch of inconsistency for a team that won 27 straight in the regular season and figured to turn this postseason into a coronation rather than a competition. But the short-handed Chicago Bulls put up an inspired fight in the Eastern Conference semifinals, the Indiana Pacers took them the full seven in a rugged conference finals and the Spurs picked them apart in three of the first five games in this series. For most of the last two months, the Heat have preferred to wait until they were in serious trouble before finding that extra gear that only they seem to have. Down 2-1 in the series, James, Wade and Bosh combined for 85 points to even the series. It doesn't get any more serious than what the Heat faced when they walked into American Airlines Arena on Tuesday night. One more uninspired performance from their three All-Stars, one more lazy night on defense, one more loss and the Heat were done for the season. The prospects of falling to 1-2 in NBA Finals appearances since James, Wade and Bosh united in 2010 loomed over a team that was constructed to win not just one title, but multiple crowns. In the unflappable Spurs, the Heat may be facing their biggest challenge yet. Duncan, Parker and Ginobili have teamed to win three championships, so they know what it takes to deliver in the finals. And youngsters like Green and Leonard have shown that even when LeBron and Co. flex their muscle, like they did in Games 2 and 4, they come right back at them. For as much as James and the Heat had riding on this finals appearance, the Spurs may have even more. Duncan is 37, while Ginobili will soon turn 36 and is in the final year of his contract, giving the feeling that after so many premature proclamations of demise for this core group, And the Spurs have played with the urgency and desperation that comes with those stakes. Game 5 was essentially a must-win for them if they wanted to avoid having to win the last two games of the finals on the road, something no team has ever done.