De La Rosa left Tuesday trailing, 4-0, but the Rockies got him off the hook for a loss by taking the lead in the sixth inning. The Rockies ended up winning, 9-8.
"Yesterday I played catch and I felt a little more pain than normal," De La Rosa said. "I don't know why. Today when I was warming up, it bothered me. It's not an excuse to not make good pitches.
"It probably was the cold [65 degrees by the Bay can be chilly with the wind]. ... It's a long time since I've pitched in this kind of weather. Probably that affected me. But like I say, I made a lot of mistakes with some hitters and I paid for it."
De La Rosa, who entered Tuesday looking to tie the Nationals' Jordan Zimmermann for the National League lead in wins (17), gave up four runs -- on a three-run homer off the left-field pole to Hunter Pence in the first inning and an RBI double from Marco Scutaro in the second -- on four hits and three walks. Righty Jeff Manship replaced De La Rosa.
It was the shortest outing for De La Rosa since July 31, 2008, during his first season with the Rockies, when he left after 1 2/3 innings in an outing that saw him give up seven earned runs on five hits and four walks.
De La Rosa first suffered a bruised left thumb June 17 at Toronto. He pitched through it that day and held the Blue Jays scoreless on one hit through seven innings. The Rockies ended up losing that game, 2-0, and De La Rosa did not figure in that decision.
In every start since, De La Rosa has admitted, the thumb has been a problem to some degree. Nevertheless, from the day he suffered the injury through his last start, a home win over the Dodgers, he was 9-2 with a 3.15 ERA in 15 starts.
De La Rosa said at the time he suffered the injury throwing a pitch, but in several games since, he has aggravated it either bunting or swinging.
Still, De La Rosa did not rule out making his next start.
Thomas Harding is a reporter for MLB.com. Read his blog, Hardball in the Rockies, and follow him on Twitter @harding_at_mlb. This story was not subject to the approval of Major League Baseball or its clubs.