ST. LOUIS – Reggie Sanders, Chris Carpenter, and the St. Louis Cardinals looked every bit like the best team in baseball – even with a shaky ending.

San Diego played as poorly as its record suggests for most of the day. And now, with ace pitcher Jake Peavy out for the postseason with a broken rib, the Padres might be overmatched.

Sanders hit a grand slam and set an NL division series record with six RBI, Carpenter pitched six scoreless innings before being pulled as a precaution, and the Cardinals built a big lead and held off the Padres 8-5 yesterday in Game 1.

Facing a team that won the West despite an 82-80 record, the Cardinals – who led the majors with 100 wins – opened an 8-0 cushion in the fifth inning against Peavy. He pitched with an injury that worsened in the third and was taken to a hospital after lasting only 4 1 /3 innings. An MRI showed one broken rib on his right side and the possibility of a second break. A Padres spokesman said the injury would take four to six weeks to heal.

Peavy thinks he might have bruised his ribs during a celebratory scrum on the field after the Padres clinched the NL West last Wednesday. He said the injury was probably worsened when he caught a spike on the rubber on a wild pitch in the third that didn’t even make it to the dirt.

Even without Peavy, the pesky Padres weren’t done. They scored once in the seventh, added another run in the eighth and then got right back into it in the ninth. San Diego scored three times and loaded the bases with two outs before closer Jason Isringhausen struck out Ramon Hernandez.

Mark Mulder will oppose San Diego’s Pedro Astacio tomorrow in Game 2 of the best-of-five series. Jim Edmonds helped St. Louis with a home run, double, and single. Eric Young had a pinch-hit homer in the eighth for San Diego and an RBI groundout in the ninth.

Manager Tony La Russa’s team won for the fifth time in six NLDS openers. That includes a victory in 1996 when the Cardinals swept the Padres.

The 37-year-old Sanders was on pace for the first 30-homer, 30-steal season of his career before missing 54 games after breaking his right leg in an outfield collision with Edmonds in mid-July. Sanders rediscovered his stroke in the final week of the regular season, driving in 10 runs in the last six games and homering three times in the final four.

Against Peavy, Sanders had both of the key hits. His two-run single off the glove of diving first baseman Mark Sweeney put the Cardinals ahead 4-0 in the third, and his grand slam into the left-field seats on a 3-0 fastball chased Peavy in the fifth.

Carpenter was 21-5 with a 2.83 ERA, the ace the Cardinals lacked in the playoffs last fall when they were swept in the World Series by the Red Sox. But he struggled in the final month, with a 9.14 ERA in his final four outings, and said he lost motivation after the Cardinals clinched the Central with two weeks to spare.

The Padres saw the dominant Carpenter again. He allowed only three singles while benefiting from three double plays from the team that led the majors.