HOUSTON - Roger Clemens could see the Houston Astros were running out of pitchers.

“As the game went longer and longer, Phil finally came up to me and said get ready and get your spikes on. I may need you,” the 43-year-old ace said. “Sometimes he jokes with me, but I knew he meant it.”

Clemens came out of the bullpen to boost his team, then Chris Burke ended the longest postseason game in baseball history with a home run in the 18th inning, lifting the Astros over the Atlanta Braves 7-6 Sunday and into the NL championship series.

The Rocket’s rescue also gave him a measure of redemption. Making his first relief appearance since 1984, he pitched three dominant innings and atoned for a poor start in Game 2.

Now, manager Phil Garner’s team gets a matchup against the St. Louis Cardinals — the same club Clemens lost to in Game 7 of last year’s NLCS.

“I love this, this is why you get off the couch to play this game,” said Clemens, who came out of retirement two years ago to pitch for his hometown club. “I’ve been fortunate to have played in a lot of big games, but it’s still exciting.”

The Braves took a five-run lead into the eighth, and were poised to send this first-round series back to Atlanta for a decisive Game 5 Monday night.

Instead, Lance Berkman hit a grand slam in the eighth and Brad Ausmus tied Game 4 with a two-out homer in the ninth barely beyond Gold Glove center fielder Andruw Jones’ outstretched glove.

Then, at 6-all, the Braves and Astros began the real endurance test that wound up lasting 5 hours, 50 minutes. The previous longest postseason game also occurred in Houston — the New York Mets clinched the 1986 NLCS with a 16-inning win at the Astrodome.

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

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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.”

When Burke hit the homer, Clemens was in the dugout tunnel with Craig Biggio, the 39-year-old second baseman who has spent his entire career in Houston.

“We were like two tired old men walking out of the tunnel, and then we were like two kids having a good time,” Clemens said. “We were holding each other up.”

The Astros get a few days to rest. The NLCS starts 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.”

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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, Clemens could not hold an early lead in Game 7, denying the Astros their first World Series appearance.

The loss marked 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.