ST. LOUIS -- It takes only one postseason to change a well-known player into something of a cult hero. Ask Carlos Beltran. Or Francisco Rodriguez.

And now, Roy Oswalt.

Oswalt, perhaps the least famous back-to-back 20-game winner in Major League history, proved on Thursday why his Houston Astros teammates view him as the ace of the pitching staff.

The right-hander had no margin for error through seven brilliant innings, holding his opponents to a single run as the Astros topped the St. Louis Cardinals, 4-1. Before a sellout crowd of 52,358 at Busch Stadium, Houston evened the National League Championship Series at 1-1.

After falling in a disappointing Game 1 loss, the Astros needed Oswalt to be Oswalt. No one was surprised at how forcefully the right-hander delivered.

"He was determined tonight," manager Phil Garner said. "He was as locked in as I've seen him. There were a couple points in the game where I thought he made a couple good pitches that were really close in key situations and he didn't get the called strike. He didn't let it rattle him."

Garner was referring to the fifth frame, when Oswalt threw at least two pitches to Jim Edmonds that could have easily been construed as strike three. Home plate umpire Greg Gibson thought differently, until the last fastball Oswalt threw to the inside corner. Strike three.

Albert Pujols led off the next frame with a solo homer, narrowing Houston's lead to 2-1, but that would be the end of the Cardinals' scoring threat.

"He makes a mistake to Pujols and just shuts them down after that," Garner said. "That's as locked as you get. When you're playing in these high-pressure situations, it can be easy to wear down. Roy didn't."

Oswalt's finest moments arrived when he appeared to be tiring in the seventh. Yadier Molina doubled to left, and pinch-hitter John Rodriguez drew a walk. After a rather lengthy conversation on the mound with pitching coach Jim Hickey, Oswalt coaxed a fly ball to center field from David Eckstein and escaped the inning when Edmonds knocked a first-pitch ground ball to Lance Berkman.

"That was the ballgame," Garner said. "That was definitely the ballgame, because we opened it up after that. That [seventh] was their shot."

"I knew it was going to be the last inning I was out there," Oswalt said. "The pitch count was getting up. It was a key situation in the game, two men on and the meat of their lineup coming up. To get out of that inning and the next inning, to have to face Pujols with no one on, was a key situation in the game."

Oswalt left the game with a lead, thanks in part to Chris Burke, who proved Garner right by giving him this rare start in left field.

"Hi, Chris Burke-tober," hitting coach Gary Gaetti chortled as Burke strode to his locker to address, for the second time this week, a herd of national reporters, many of whom had never heard of him before last Sunday.

Burke, who homered in his previous two postseason at-bats, tripled to right-center field with one out in the second and scored on catcher Molina's passed ball.

Burke also helped turn a one-run lead into a three-run victory during the eighth inning while facing St. Louis reliever Julian Tavarez. Berkman doubled to right, but was frozen when both Morgan Ensberg and Jason Lane grounded to short. Berkman advanced to third on Tavarez's wild pitch, and Burke drove in the run with a base hit to left.

Adam Everett tripled to left, allowing Burke to plate the fourth and final run.

"He prepares himself very well, and a lot of that goes unnoticed because people aren't here to see that," Everett said of Burke. "He's a big-time player. He likes the spotlight."

Thursday's win was the Astros' first NLCS road victory over the Cardinals, dating back to last season. The Cardinals won all four games at Busch Stadium during the seven-game series.

Leaving St. Louis with a 1-1 split was signficant, considering they left here 0-2 this time last year and then won all three games in Houston.

"It's important," Garner said of the split. "We beat them here, and we haven't done that for a while in these [playoff] situations. They know that, and we know that, too. It's not going to make any of these games any easier, but there's a measure of confidence there that says, 'Yes, we've done it.'

"We'll have to play hard, we'll have to play good baseball. But tonight, this was as good a game as it gets."