SAN DIEGO -- A rough start to his major league debut was all Josh Geer needed to settle down.
But it didn't start out too well for Geer. The right-hander gave up singles to the first two batters he faced before getting out of a jam with runners at second and third and no outs without allowing a run.
"In a weird way, I like having guys on second and third," he said. "It makes me more focused. I just stuck to my game plan and just tried to hold them off."
Geer, subbing for Jake Peavy, got six runs from the Padres in the fourth inning, two coming on Brian Giles' single, for a 6-2 lead.
"You're supposed to keep the same mentality like it was a tie game," Geer said. "But it got me more relaxed."
The loss prevented the Rockies from moving within five games of first-place Arizona in the NL West. The Diamondbacks lost 6-2 to the Los Angeles Dodgers.
Colorado lost for the fourth time in 13 games.
Geer (1-0) allowed two runs and five hits with three walks and five strikeouts. He needed 105 pitches to get through the minimum number of innings for the win.
Geer, a third-round draft pick in 2005, became the 11th San Diego player to make his major league debut this season, including five pitchers.
"(Geer) changed speeds and kept the ball out of the middle," Rockies manager Clint Hurdle said. "There wasn't enough in the recipe for us to win."
Peavy was originally scheduled to start on Saturday but was pushed back one day after throwing 121 pitches in his last start.
Geer gave up game-opening singles to Clint Barmes and Willy Taveras with Barmes taking third. Taveras stole second and the Rockies had runners in scoring position with no outs and their Nos. 3-5 hitters coming up.
Geer got Matt Holliday to hit a comebacker to the mound for the first out. He then struck out Brad Hawpe and Garrett Atkins to get out of the inning
"There's a great confidence with the way he carried himself in the first inning," San Diego manager Bud Black said about Geer. "That was a great sign."
Rookies Will Venable and Edgar Gonzalez each drove in two runs as San Diego (51-83) won for the fourth time in five games. The Padres are attempting to avoid 100 losses for the sixth time in team history and the first time since 1993.
Ubaldo Jimenez (9-12) held the Padres hitless through three innings before his lack of control hurt him in the fourth, when he walked four.
After giving up a leadoff double to Luis Rodriguez, Jimenez issued consecutive one-out walks to load the bases. Venable, who made his major league debut on Friday night and got a hit in his first at-bat, drove in his first run with a bases-loaded single.
"I was ahead in the count and I just wanted to get something that I could hit," Venable said.
Gonzalez drove in another run on a forceout. Jimenez then loaded the bases with a walk to rookie Nick Hundley before forcing in a run by walking Geer.
Glendon Rusch replaced Jimenez and gave up a two-run double to Giles and Rodriguez's RBI single for a 6-2 lead.
Jimenez gave up six runs on only two hits but gave up five walks in 3 2/3 innings.
"It was one of those crazy things that happens," Jimenez said. "I just lost the strike zone and I couldn't find it. I couldn't find the rhythm."
The Rockies scored off Geer twice in the second on consecutive two-out, RBI singles by Barmes and Taveras for a 2-0 lead.
Barmes added a two-run triple in the ninth.
Colorado dropped to 18-8 against rookie starters this season.
The Rockies have not been within five games of the NL West lead since April 21. ... The 11 San Diego players who have made their major league debuts this season is five shy of tying the team record, set in 2002. ... Padres OF Jody Gerut was held out of the lineup for a second straight game with to a sprained left finger. It is not certain how long Gerut will be out. ... Venable tripled in his first major league at-bat on Friday night, he joined John Sipin as the only two Padres to accomplish the feat. Sipin did it on May 24, 1969.