The Giants, who trail Arizona by seven games in the National League's West Division and are six games behind the Atlanta Braves in pursuit of the league's wild card berth, opened the series Thursday with an 8-5 win.
Pablo Sandoval hit for the cycle and finished 4-for-4 for San Francisco.
Sandoval became the first Giants player to hit for the cycle since Fred Lewis accomplished the feat on May 13, 2007, also at Coors Field. Sandoval also became the 23rd player in Giants franchise history to do it and only the 10th since the club moved to San Francisco.
Sandoval picked up the first leg of the feat when he blasted a pitch from Rockies starter Jhoulys Chacin over the right field wall for a two-run homer in the opening inning. He singled up the middle in the second and ripped a double to left to start the fifth.
He came up to attempt the hardest part of the cycle in the sixth against Chacin. He drove a high fastball into the right-center field gap. The ball hit high off the wall and caromed away from right fielder Carlos Gonzalez, allowing Sandoval to hustle all the way and dive head first into third base.
Brandon Belt cracked a solo home run, Cody Ross picked up two hits, including an RBI double. Brandon Crawford added two hits and a run scored for the Giants, winners of five straight.
Ryan Vogelsong (11-7) gave up two runs on four hits over 5 1/3 innings while fanning eight and walking four. He also chipped in offensively with a pair of hits and two runs scored.
Chacin (11-12) was tagged with the loss after going 5 2/3 innings, giving up seven runs -- four earned -- on nine hits while walking four and striking out one.
Tonight, it will be Bumgarner, who won seven games for the Giants in 2010 and has won four consecutive starts since dropping a 7-5 verdict at Houston on Aug. 20.
He's subsequently beaten Houston, the Chicago Cubs, San Diego and Los Angeles while allowing 17 hits and four runs in 27 2/3 innings.
The 22-year-old hasn't beaten the Rockies in five starts, going 0-3 with a 3.00 earned run average in 30 innings.
San Francisco is 6-4 in his last 10 starts.
For the Rockies, former first-round pick Alex White makes start No. 8 of his rookie season.
The 15th pick of the 2009 draft debuted with the Cleveland Indians on April 30 and made three starts in the American League, then came to Colorado as part of the trade deadline deal for Ubaldo Jimenez.
He was 0-1 with a no-decision in his initial two outings with the Rockies, but has beaten San Diego and Cincinnati in his last two starts on Sept. 3 and 10 while allowing 13 hits and 11 runs in 10 innings.
Colorado is 3-1 in his four NL starts and has outscored its foes, 26-22.
San Francisco has won eight of 12 versus Colorado this year and 12 of the last 17 meetings overall.