The Rockies won, and they did it without slugger Matt Holliday in the lineup.
Padres' starter Jack Cassel was the first to feel their wrath.
Cassel exited after just 2 1/3 innings of work. Cassel, who had already allowed two runs, had two on the bags in the top of the third, which was one too many for the Padres. They didn't want to take any more chances, so they pulled Cassel and brought in reliever Justin Hampson, who immediately allowed an RBI single to Brad Hawpe.
"Every team in this division is a good-hitting ballclub," Cassel said. "They're all Major League-caliber hitters, and when you don't execute your pitches they're going to be able to put good swings on them, and tonight they were falling in for them.
"I had a couple sinkers that ran back over the plate for me; the ball didn't stay down as much. They had a little more run than sink tonight."
Said manager Bud Black: "I think he was a little bit up in the zone overall, and the changeup command wasn't there like his last start."
The Rockies built a 3-0 lead thanks to Hawpe, who drove in two and later finished the night by piling on four hits to tie his career high.
But the Padres came back in the fifth inning by plating two runs. Khalil Greene led off with a home run -- his 24th of the season -- to get the Padres on the board. Later in the inning, Brian Giles drew a bases-loaded walk to force in Josh Bard to cut the lead to 3-2.
With one out and the bases still loaded, the Padres were unable to do anything else as Mike Cameron struck out and Scott Hairston -- who came in to pinch-hit and later stayed in the game in left field for Milton Bradley -- popped out to second baseman Kazuo Matsui to end the inning.
Colorado would later widen its lead by scoring three more times. Two of them came in the top of the eighth, when Cameron dropped pinch-hitter Joe Koshansky's fly ball.
The 35,020 in attendance at PETCO Park watched the Rockies (83-72) come out with the victory to cement a series win, while the Padres (85-69) dropped their second consecutive contest.
Bard went 2-for-4 and was part of one of the best plays in the game in the first inning, when he tagged Todd Helton out at home for the third out of the inning, taking a strong relay throw from Greene.
Cassel (1-1) allowed three runs on six hits, while Rockies starter Mark Redman yielded two runs on four hits over 4 1/3 innings of work. Reliever Ryan Speier (2-1) got the win, coming on in the fifth to squelch the Padres' rally.
"We are looking forward to tomorrow," Black said. "Anytime you play meaningful games this time of year, I think we are all excited; it's good stuff. This is what players love. This is why we play.
"I know there's a lot of other teams that would love to be in games like we're playing right now. So we'll come out tomorrow and let it all hang out."
Gonzalez, who went 0-for-3 on Saturday, said the Padres will be ready.
"We should be in the playoffs, so there's no need to panic or anything," Gonzalez said. "Still got eight games to go. We don't need a win to get momentum or anything. We need to win because the only way to get in the playoffs is to win games.
"Still got to believe, right?"