"I knew once I fixed the mechanical part, things would come back to where they need to be," Cook said, noting he had worked with pitching coach Bob Apodaca over the past couple weeks to correct a tiny flaw in his release point. "Just breaking down my mechanics a little bit and fixing that one little thing made a huge difference. If I just keep doing that, I'll be a lot more consistent and give our team a chance to win some more games."
Colorado manager Clint Hurdle was encouraged by the solid outing from the team's No. 1 starter.
"I thought he was able to maintain and repeat his delivery solidly for six innings," Hurdle said. "He got the ball up a little bit in the seventh, really the only time in the whole game he got some pitches up. But it was a quality start and it was very, very good to see. He's our guy. He's our ace."
Adrian Gonzalez homered twice for San Diego, which fell behind 7-0 and lost for the fourth time in five games.
Gonzalez's seventh career multihomer game pushed his season total to nine, a Padres record for April.
Cook (1-1) allowed three runs and five hits and struck out three in beating the Padres for the 12th time in 16 decisions. He earned his 53rd career victory with the Rockies, tying Pedro Astacio for second on the team's list.
The key, Cook said, was his ability to keep his sinker down in the zone, with only a couple of exceptions which Gonzalez and Henry Blanco tagged for home runs in the seventh.
"Today, I predominantly used my sinker," he said. "I threw only three breaking balls and I felt like my old self. I got a lot of pitches down in the zone. I got a couple pitches up and those were the ones that went over the fence."
The win was his first since Aug. 29, 2008, at San Diego, ending an eight-start string in which he had gone 0-2 with six no-decisions.
"We didn't give up. We had some good at-bats at the end. This was encouraging," Gonzalez said. "[Cook] kept the ball down low and was aggressive. He uses both sides of the plate. You don't always know if you'll see fastballs or sinkers. He gets you to swing at pitches you normally don't want to swing at."
Huston Street earned his second save.
Kevin Correia (0-2) went five innings and allowed three runs and six hits, including home runs by Helton and Iannetta.
Helton added a two-run single and Iannetta had an RBI single as part of a four-run sixth that gave the Rockies a 7-0 lead.
But Colorado had to withstand a late rally to win a series for the first time since taking the season-opening series against Arizona.
"That's what you shoot for going into a series. That was a pretty big game for us today and Cookie set the tone," Helton said.
The Padres are midway through a stretch of 17 games in 17 days, with their next day off on May 11. ... Gonzalez's extended his hitting streak to 11 games. ... LHP Arturo Lopez made his major league debut when he came on with two outs in the sixth. He failed to retire any of the four batters he faced, walking two, hitting one and giving up Helton's bases-loaded single. ... The Rockies placed INF Jeff Baker (left wrist sprain) on the DL and recalled OF Matt Murton from Triple-A Colorado Springs. Murton struck out in the seventh as a pinch hitter. ... Jason Jennings has the most wins in Rockies' history (58).