De La Rosa (0-3) had one poorly located pitch early -- Tommy Medica's leadoff home run in the second -- but otherwise made a good percentage of his pitches while giving up three runs (two earned) on seven hits (two damaging infield hits in the fifth), with four strikeouts and a walk.
"I feel good, but we still lost the game," De La Rosa said. "No matter how I did, it's my fault when a mistake is made and we lose the game."
Medica's first homer of the season tied the score, 1-1. That was big against De La Rosa, who has held the Padres to a .213 batting average in eight games, including five starts, at Petco Park.
"De La Rosa has been tough on us over the years," Padres manager Bud Black said. "He's a solid pitcher. I think that home run by Tommy swung the momentum back toward us."
De La Rosa also didn't receive nearly enough help.
The Rockies' Justin Morneau went 3-for-3 with a second-inning homer off Andrew Cashner (2-1), a double and a sacrifice fly in the eighth. Nolan Arenado celebrated his 23rd birthday with two standout defensive plays -- a deft backhand pickup to start a double play in the third and a dive to rob Xavier Nady to end the fifth.
But as has been the case with the Rockies during a road trip that has seen them go 2-4 -- with Thursday afternoon's finale of the four-game set with the Padres remaining -- the big inning was lacking. With bases loaded and one out in the sixth, Cashner, who gave up nine hits but just one earned run while striking out five in 7 1/3 innings, induced a double-play grounder from Jordan Pacheco.
"You don't get a lot of opportunities against a guy like that," Rockies manager Walt Weiss said. "You hope somebody gets a big hit or you get one to drop when you do get some baserunners.
"He's got a real hard sinker and it's easy to beat that thing into the ground. That's what he did. He got a double-play ball in that situation."
The Rockies were 1-for-9 with runners in scoring position.
The Padres took a 3-1 lead with two two-out runs in the fifth. However, Alexi Amarista's one-out single and Everth Cabrera's single with two down didn't leave the infield. Cabrera's bounced off home plate. The first of the runs scored on a passed ball by Pacheco, the second on Chris Denorfia's double.
Meltdowns after misfortune marred De La Rosa's first three outings. But after escaping the fifth, he struck out two in a spotless sixth and finished with 90 pitches. He lasted 4 1/3 innings in each of his three previous starts.
"It was a solid outing by Jorge," Weiss said. "You pitch like that, you give us a chance to win. There's not a lot of margin for error with Cashner on the other side, but Jorge did a nice job."
Reliever Tommy Kahnle walked leadoff man Amarista in the seventh and saw him score on Denorfia's single.
The Rockies fell to 3-7 on the road but can gain a split against the Padres with a win Thursday.