DENVER -- It took Scott McClain 19 seasons to hit a major league home run. When he got his first one Wednesday, he soaked it in.
"As it was leaving it was a moment of relief," the 36-year-old rookie said. "I'm glad I hit one that was a no-doubter."
McLain's home run backed Barry Zito, who won for the third time in four starts. Nate Schierholtz also had a career-high four hits as the San Francisco Giants slowed the Colorado Rockies with a 9-2 victory Wednesday.
McClain, who has hit 287 homers in 1,664 minor league games, hit a solo home run in the sixth inning.
"All the hard work he's put in, all the home runs he's hit in the minor leagues, to get one here, the team was just elated for him," Giants manager Bruce Bochy. "It makes it all worthwhile."
McClain had three hits and drove in three runs in his first start since being called up from Triple-A Fresno on Tuesday.
"The Giants calling me up the past two Septembers makes the hard work pay off and makes it worth it," he said.
McClain has been with seven major league organizations and played four years in Japan. He signed with San Francisco in January 2007 and hit .300 with 29 homers and 108 RBIs for Fresno this year.
"The last three or four years, I've said this is my last season going in, but for some reason I end up putting up fairly decent numbers, and it makes it worth it to come back," said McClain, who has played in just 32 major league games.
Hoping to duplicate last season's dazzling September run, Colorado had won seven of 10, including the first two games of the three-game series. The NL champion Rockies began the day five games behind NL West-leading Arizona.
"You would have liked to go out there and put a sweep on those guys, but Zito has a lot of pride," Rockies manager Clint Hurdle said
Zito (9-16), who lost his first nine decisions this year, allowed two runs and four hits in eight innings, throwing a season-high 123 pitches.
"I was in a good rhythm," he said. "I wanted to capitalize and keep going."
Zito felt strong after eight innings but wasn't disappointed he didn't pitch the ninth.
"A complete game would have been great, but I did what I wanted to do out there and we had a big lead," he said
Pablo Sandoval hit his second home run of the year for the Giants, who had lost five straight and seven of eight.
"We needed that one," Bochy said. "It's been a rough trip. Coming off a tough game last night and we hadn't won a game on this trip. We definitely needed this."
Aaron Cook (16-9) allowed six runs and 10 hits in three innings, his shortest outing since Aug. 7, 2004.
"Today was a definitely a big game for us to come out and win, and I didn't hold up my end of the bargain," Cook said.
Aaron Rowand and Travis Ishikawa hit run-scoring singles in the first. Jeff Baker's RBI grounder cut the deficit in the second, but San Francisco made it 6-1 in the third on McClain's RBI single, Ishikawa's two-run double and Emmanuel Burriss' run-scoring single.
Clint Barmes homered in the fifth to make it 6-2, but Sandoval and McClain hit back-to-back homers off Steve Register in the sixth.
Dexter Fowler, a top outfield prospect for Colorado, flied out in his first major league at-bat. ... Cook has also allowed 13 runs in the first inning this year. ... Giants SS Omar Vizquel is hosting an exhibit of his paintings in San Francisco on Thursday. Vizquel will donate a percentage from his paintings sold to the Giants Community Fund.