LOS ANGELES — St. Louis Cardinals manager Mike Matheny has been trying to pick his spots in terms of when to give 36-year-old first baseman Lance Berkman days off because of his history of knee problems.

Now, he may not have a choice.

Berkman left Saturday night’s game with an injured right knee after stretching for a throw from shortstop Rafael Furcal on Justin Sellers’ groundout for the third out of the second inning. Matt Carpenter took over at first and committed a fielding error on a hard-hit grounder by former Cardinal Adam Kennedy in the fourth, allowing the game’s first two runs to score in Jake Westbrook’s 6-0 loss to Clayton Kershaw and the Los Angeles Dodgers.

“You go up against a lineup like that and against a pitcher like Kershaw and you know that any kind of mistake is probably going to cost you. And it did,” Matheny said. “That was a play that can be made — and most often would be made — but it didn’t happen and it ended up costing us a couple of runs. Pitchers are going to start thinking that they need to do more when the plays aren’t made behind them.”

Westbrook (4-3) was charged with four runs — three earned — and six hits in 6 1-3 innings. The 34-year-old right-hander, pitching at Dodger Stadium for the first time in his 12-year career, departed after giving up Kershaw’s opposite-field double off the glove of left fielder Matt Holliday. It was Kershaw’s first extra-base hit after hitting 28 singles over five seasons.

Tony Gwynn Jr. greeted Eduardo Sanchez with a single that drove in Kershaw. The Dodgers got two more runs that inning when Gwynn scored on Sanchez’s wild pitch and Andre Ethier added an RBI single that increased his NL-best RBI total to 36.

Westbrook knew he would have his work cut out for himself facing the Dodgers’ ace, but he didn’t let that distract him.

“You try not to do that, because you always want to go out there and throw a decent ballgame and put up zeros no matter who you’re facing,” Westbrook said. “If you put too much added pressure on yourself, it’s really counter-productive. So you just go out there and pitch your game and do the best you can.”

Berkman had just come off the disabled list last Sunday after being sidelined for 21 games because of a strained left calf he aggravated while chasing a popup. Another trip to the DL is a distinct possibility, judging by the way he was limping around in the clubhouse. — Agencies