WASHINGTON – Chris Carpenter was every bit the postseason ace he’s been in the past for the St. Louis Cardinals.

Taking the mound for only the fourth time in 2012 and missing a rib after surgery to cure numbness on his right side, the 37-year-old Carpenter pitched scoreless ball into the sixth inning while rookie Pete Kozma delivered a three-run homer and the defending champion Cardinals beat the Washington Nationals 8-0 on Wednesday to take a 2-1 lead in their NL division series.

All in all it was quite a damper on the day for a Nationals Park-record 45,017 red-wearing, towel-twirling fans witnessing the first major league postseason game in the nation’s capital in 79 years.

Three relievers finished the shutout for the Cardinals, who can end the best-of-five series Thursday in Washington.

“We’re not out of this, by a long shot,” Nationals Manager Davey Johnson said. “Shoot, I’ve had my back to worse walls than this.”

The Cardinals won 10 fewer games than the majors-best Nationals and finished second in the NL Central, nine games behind Cincinnati, sneaking into the postseason as the league’s second wild card. But the Cardinals become a different bunch in the high-pressure playoffs — no matter that slugger Albert Pujols and Manager Tony La Russa are no longer around.

Carpenter still is, even though even he didn’t expect to be pitching this year when he encountered problems during spring training and needed an operation in July to correct a nerve problem. He returned Sept. 21, going 0-2 in three starts, so it wasn’t clear how he’d fare Wednesday.

“I’m not going to go out there and compete,” Carpenter said, “if I’m not good enough to compete.”

He was good enough, allowing seven hits and walking two in 52/3 innings to improve to 10-2 over his career in the postseason.

“He pitched well today,” Washington’s Jayson Werth said. “We had him in some spots. We had him on the ropes a couple of times. We were just one bloop away from a totally different ballgame.”

Carpenter was pretty good with a bat, too, collecting a pair of hits, including a double that just missed clearing the wall.

Similarly, neither club could be sure which Edwin Jackson would show up for Washington, a year after he was part of the Cardinals’ 2011 championship team: The one who struck out 10 and allowed one unearned run in eight innings against St. Louis on Aug. 30, or the one who lasted only 11/3 innings in a loss to the Cardinals on Sept. 28.

Much closer to the second version; he was done after five innings and four runs.

“I just missed across the plate with a couple of balls and it cost me,” Jackson said.

The Cardinals tacked on four runs off three relievers.

The spirited crowd booed when Washington’s Danny Espinosa was ruled out at first after bunting in the second. Replays showed he did beat third baseman David Freese’s throw, but the call was missed by Jim Joyce — an umpire best known for blowing a call at first base to ruin Detroit pitcher Armando Galarraga’s bid for a perfect game in 2010.

The Cardinals opened the second inning with four consecutive hits, the biggest being Kozma’s homer to make it 4-0. Kozma took over as the Cardinals’ everyday shortstop in September, replacing injured All-Star Rafael Furcal.

NOTES: Frank Robinson, the Nationals’ first manager, threw out the ceremonial first pitch. Former Senators slugger Frank Howard gets that honor Thursday. Wednesday was the 88th anniversary of Washington’s only World Series championship, won by the Senators on Oct. 10, 1924.