HOUSTON – Roger Clemens and the Houston Astros gave a whole new meaning to the word “longevity.”

The 43-year-old Rocket came out of the bullpen to rescue the Astros and Chris Burke ended the longest postseason game in baseball history with a home run in the 18th inning, lifting Houston over the Atlanta Braves 7-6 yesterday and into the NL championship series.

“I’m sure proud of the guys,” Clemens said. “It’s been a lot of work for us. How ’bout the kid?”

Standing next to Clemens, the 25-year-old Burke was beaming.

“I’m just glad I could do my part,” Burke said. “It was draining, mentally draining.”

The Braves took a 6-1 lead into the eighth, and were poised to send the series back to Atlanta for a decisive Game 5. Instead, Lance Berkman hit a grand slam in the eighth and Brad Ausmus tied it with a two-out homer in the ninth barely beyond center fielder Andruw Jones’s outstretched glove.

Then, at 6-6, the Braves and Astros began the real endurance test that wound up lasting five hours, 50 minutes. The previous longest postseason game also occurred in Houston – the Mets clinched the 1986 NLCS with a 16-inning win at the Astrodome.

With Clemens pitching three scoreless innings in his first relief appearance since 1984 – and this time atoning for a poor start in Game 2 – the Astros advanced to play the St. Louis Cardinals in the NLCS starting Wednesday night at Busch Stadium.

“If he comes in a game like that, you know it has to be important to him,” Jones said. “He was going to try not to make any mistakes, and he didn’t. He pitched great.”

Clemens gave up one hit and struck out four, setting up the first NLCS rematch since Pittsburgh and Atlanta played in 1991-92. Last October, the Cardinals beat Clemens in Game 7, denying the Astros their first World Series appearance.

And it was another early October exit for the Braves, who have won an unprecedented 14 straight division titles but have just one World Series crown to show for it. The Astros eliminated Atlanta last year.

“It never feels good, but I’ve had a couple of heartbreakers where I could have won the game, but instead ended the season,” Chipper Jones said. “You learn from that.”

The Braves wasted an early grand slam by Adam LaRoche. Berkman’s shot made this the first postseason game ever with two slams.

Burke entered the game in the 10th inning as a pinch-runner. He came up with one out in the 18th against rookie Joey Devine, and launched a drive over the left-field wall.

Burke was mobbed his teammates at the plate after only the sixth series ending home run in history, and the first since Aaron Boone sent the Yankees over Boston in the 11th inning of Game 7 in the 2003 ALCS.