ST. LOUIS (Ticker) -- The St. Louis Cardinals and the San Diego Padres both needed their aces to be at the top of their game. Only Chris Carpenter delivered.

Carpenter pitched six scoreless innings and the Cardinals hammered Jake Peavy for eight runs en route to an 8-5 victory over the Padres in Game One of the National League Division Series.

Reggie Sanders hit a grand slam and recorded a franchise postseason-record six RBI for NL Central champion St. Louis, which was 18 games better than NL West champion San Diego in the regular season.

Despite the discrepancy in records, the Padres figured to have a chance in the series because of Peavy, the NL strikeout king scheduled to start twice in the best-of-five series.

San Diego's hopes for an upset took a serious blow after the game as Peavy was diagnosed with a broken rib and will miss the remainder of the postseason.

Although he won 21 games, Carpenter entered the postseason as a question mark after fading down the stretch. The righthander went 0-1 with a 9.14 ERA in his last four starts.

Carpenter (1-0) showed the form that made him a leading candidate for the NL Cy Young Award on Tuesday, allowing three singles and three walks before leaving after the sixth inning because of cramps in his right hand.

He struck out three, threw 57 of 91 pitches for strikes and got San Diego to hit into three inning-ending double plays.

"I felt like after the second I started to settle down and get the ball down in the strike zone and make the quality pitches I had to make," Carpenter said. "We had three key double plays that stopped some rallies and I felt I made pitches when I had to."

Peavy (0-1) was not sharp, surrendering a solo homer to Jim Edmonds in the first and three more in the fourth, highlighted by Sanders' two-run single.

"With a guy like (Peavy) you need to get him early because if he starts feeling comfortable out there on the mound he's going to start making his pitch," Cardinals first baseman Albert Pujols said.

The Cardinals chased Peavy one inning later. Edmonds and Albert Pujols reached on a pair of one-out singles and Larry Walker was walked intentionally for Sanders, who connected on a 3-0 pitch to make it 8-0.

"It was one of those situations where Peavy was having a tough time locating the ball and on 3-0, I just was looking for an area where I could get the bat extended," said Sanders, who set an NLDS record with his six RBI. "It was there and I was able to get on top of it and drive it."

"He pitched himself into trouble with a walk and got behind with Sanders and that's putting yourself in a tough jam," Padres manager Bruce Bochy said. "But the first three innings he was throwing the ball well."

After missing nearly two months due to a broken right leg, Sanders began to heat up in the final week of the regular season with 10 RBI in his last six games.

"One thing we felt about coming in this last homestand, we had some key guys including Reggie starting to take better at-bats," St. Louis manager Tony La Russa said. "He'd been out a long time. When you face a guy like Jake Peavy and you get an advantage 3-0, you may only get one strike to hit so he had the green light."

San Diego made things interesting against St. Louis' bullpen. Khalil Greene 's sacrifice fly in the seventh off Brad Thompson put the Padres on the board and Eric Young led of the eighth with a pinch homer off Randy Flores .

Cal Eldred , who got the final out in the eighth, allowed two hits in the ninth. La Russa turned to closer Jason Isringhausen , who let both runners score before Brian Giles cut the deficit to 8-5 with a run-scoring single.

"I wanted to make sure I didn't walk anybody so I just threw strikes," Isringhausen said. "I got them to hit a couple decent pitches. They hit a couple bad pitches but we got the win and that's all that matters."

Robert Fick followed with a single to bring the potential go-ahead run to the plate, but Isringhausen struck out Ramon Hernandez on three pitches for the final out.

"I've got to give the guys credit, they came out and swung the bats when we were down that many runs," Padres left fielder Ryan Klesko said. "Everybody's getting a little comfortable, a lot of guys had good approaches up there and got some hits later in the game. That's key to get the butterfies out.

"These guys battled, we were one hit away, one double or homer away from either winning or tying the game. When you're down 8-0 that's pretty good."

Peavy, who yielded eight hits in 4 1/3 innings, had allowed three runs or less in each of his last 11 starts. He failed to make it out of the fifth inning in only one of his 30 starts this season.

"We had a solid game and we got a couple of breaks against one of the top pitchers in the National League," Edmonds said. "So I'd say we're very fortunate but we played a very good game."

Carpenter required 23 pitches to get through the first and allowed the first two batters to reach in the second. But he needed just one pitch to get Greene to fly out before inducing a double-play grounder from Joe Randa to escape unscathed.

The Padres threatened again in the third. After Dave Roberts and Ryan Klesko hit consecutive one-out singles, Mark Loretta hit a sharp one-hopper right at third baseman Abraham Nunez , who stepped on third and threw to first for another double play.

"We had guys on pretty much the whole game," Klesko said. "Guys took some good at-bats out there, Carpenter pitched out of a couple innings where we had a chance to score."

"I thought early on I got away with a couple of pitches, but we made some nice defensive plays," Carpenter said.

Game Two is here Thursday with the Cardinals sending Mark Mulder to the mound. The Padres counter with veteran Pedro Astacio .

"It's always good to win the first game but you still have to win two more games and that's our goal," Pujols said. "We'll come back Thursday strong and try to get another win."

"No one gives us a shot," Giles said. "Today we battled back. We'll take tomorrow off, regroup, and Thursday's going to be a huge game for us."