"In Chase's case, he's been going at it as hard as anyone in the league since coming back from the DL," said Padres manager Bud Black.
Headley is 5-for-26 on this road trip and 3-for-14 in the first three games of the series against the Rockies. Black said Sunday was the right day to sit him, though he was available to pinch-hit. Utility man Alexi Amarista got his first start of the season at third base.
"It does him justice to get a start off," Black said.
Headley, who led the National League in RBIs (115) last season and won the Silver Slugger Award, is now hitting .230 with five home runs and 18 RBIs.
Last week, Headley talked about his struggles.
"It's a combination of things. First and foremost, I've got to swing at better pitches," he said. "I'm getting myself out. I'm making [the opposing pitcher] throw one quality strike. And there has been a little bad luck mixed in there, too."