The middle finger cut he suffered during his previous start, when he gave up 11 hits in five innings of a no-decision against the Padres, was not a factor, De La Rosa said.
"They had a lot of hitters that I hadn't faced very many times," said De La Rosa, who did not meet with reporters after the game. "They didn't swing at breaking balls. They waited for me to throw the fastball.
"Then I made a mistake with Ryan Zimmerman [on a fifth-inning RBI double that gave the Nationals a 2-0 lead]. I didn't think he was going to swing at my changeup, so I tried to throw it for a strike, and he hit it hard."
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.