But Cook (16-9) struggled, giving up two RBI singles to Scott McClain and a one-run single and a two-run double to Travis Ishikawa. Pablo Sandoval knocked a two-run shot in the sixth, followed by a McClain homer -- both off reliever Steven Register.
Note to coaches and parents of young hurlers:
Tell them to throw good strikes.
"I threw a lot of strikes," said Cook (16-9). "I didn't labor. I didn't throw enough pitches to labor. They were hitting the balls through the holes in the infield, and when I got the ball up, they were hitting it hard down the line or over outfielders' heads. It was pretty simple."
Cook remained one win shy of the club single-season record of 17, shared by Kevin Ritz (1996), Pedro Astacio (1999) and Jeff Francis (2007). With four more starts, 20 is at least within reach.
But for the amount of success Cook has experienced this season, there is legitimate concern.
Cook won 11 games before the All-Star break and threw three stirring innings on less-than-normal rest in the Midsummer Classic. But it hasn't been easy since then.
Cook wound up having to back out of an Aug. 14 start against the D-backs with back soreness. He prides himself on eating innings, but he has gone fewer than seven innings in five of his last six starts.
This season, Cook has thrown 191 innings, already second-most in his career. If he throws as he and the Rockies expect, he'll eclipse the career high of 212 2/3 he established in 2006. But if he is fatigued or still experiencing residual back trouble, he'll have to pitch better than he did Wednesday.
Manager Clint Hurdle acknowledged that Cook is one of several workhorse pitchers experiencing a down period.
"That's the challenge you have with guys that pitch innings, have strong first halves, run up decisions and stay on the mound a long time," Hurdle said. "But by the same token, that's part of taking the next step and becoming an established guy in the rotation."
The brightest spots came out of the bullpen. Matt Herges, returning from back problems that forced him to the disabled list, threw a seven-pitch seventh inning and struck out one. Ryan Speier added a clean eighth. Jason Hirsh, pitching in the Majors for the first time since suffering a broken leg last Aug. 7 and on the recovery trail for a rotator cuff strain that has marred this season, threw a spotless ninth.
A Giants workhorse-type, left-handed starter Barry Zito (9-16), held the Rockies to four hits and struck out five in eight innings. Garrett Atkins doubled and scored on a fielder's choice for the Rockies in the second inning and Clint Barmes knocked a solo shot, his seventh home run of the season, in the fifth.
"Look at all the decisions Zito's got," Hurdle said. "He hasn't been his best, but today he comes out, works quick, changes speeds, throws pitches well into the hundreds [123 on Wednesday].
"You don't want to look for excuses first, but you've got to be realistic about the condition your people are in. Aaron will be the best evaluator of that. If fatigue is not an issue, we've got to find a way to dig it out of the dirt with him."