De La Rosa (10-8) struck out seven and held the Giants to three hits, retired the last 11 batters he faced and drove in a run with a fourth-inning single. He needed to do all that because Giants starter Barry Zito (10-17) pitched well -- three runs (two earned) in eight innings.
The victory won't get the Rockies above .500 in a disappointing season, which followed last year's surprise World Series berth, but it assured them of finishing in third place in the National League West and rendering the Giants in fourth.
So, what happened for those three pitches?
"I don't know what happened," De La Rosa said. "Maybe I'm overthrowing a little bit?"
Manager Clint Hurdle quipped, "You stay in the game long enough, you see new things every day."
Later, De La Rosa had a smoother explanation of his roundabout way of, well, retiring the first batter of that inning.
"That was the plan," he said, laughing.
De La Rosa proved this season that he's capable of looking bad for a period, but just as capable of making up for it.
De La Rosa was in and out of the rotation early and had a 7.26 ERA at the All-Star break. He was dropped again briefly in August. But he finished his season with a 4.92 ERA, and this is his first Major League winning season.
"I think it's good for everybody -- good for the team, good for me," said De La Rosa, who pitched in the Majors with the Brewers and Royals previously and began this year with the Royals' Triple-A affiliate in Omaha before joining the Rockies in an April 30 trade for cash considerations.
Iannetta, who will trade a few bad pitches for what turned out to be a dominating win, is excited about the role De La Rosa could have in what the Rockies hope is a 2009 rebound.
"I'm interested to see how he shows up in Spring Training," Iannetta said. "If he shows up the same as how he finished this year, he's going to be something special. If he gets better, he's really going to be fun to watch."
The Rockies' Matt Holliday knocked a first-inning single to drive in Troy Tulowitzki, who took second on shortstop Ivan Ochoa's error -- for bumping into second baseman Eugenio Velez as he attempted to catch Tulowitzki's popup.
De La Rosa singled with two on to drive in a run in the fourth. Clint Barmes led off the seventh with a solo shot to left-center and established a career single-season homer high with 11.
Rockies reliever Manuel Corpas gave up a run in the eighth, when Nate Schierholtz led off with a double and scored on John Bowker's single. Brian Fuentes gave up a hit and a walk in the ninth, but struck out two and earned his 30th save and his 17th consecutive conversion of a save opportunity.