Denver, CO – Pablo Sandoval homered twice during an eight-run high six longballs in a 12-5 romp.
San Francisco completed its first four-game sweep at Coors Field since August 26-29, 2002, and extended its winning streak to a season-best eight games.
"It was a great series for the offense," said Giants manager Bruce Bochy.
The Giants are still five games behind the NL West-leading Arizona Diamondbacks, but closed to within four games of Atlanta in the wild card race.
Despite the rare run support, Cain (12-10) labored through five innings, tossing 111 pitches. The right-hander gave up five runs -- three earned -- on five hits and walked four.
The Giants averaged just 3.27 runs in Cain's previous 31 starts this season.
"The game boils down to this obviously; they hit six home runs that accounted for 10 of the 12 runs that they got. That's it. There's very little else to say," Colorado manager Jim Tracy said.
The Giants took a 2-0 lead when Andres Torres led off the game with a walk and scored on Fontenot's home run to right field.
San Francisco resumed its power surge after Smith's sacrifice fly in the third.
Sandoval opened the fourth with a drive to left-center and Belt went deep two batters later. Crawford then doubled and scored on Cain's fifth career home run, a two-out smash over the center-field wall.
After Torres walked and Rogers plunked Fontenot, Carlos Beltran hit an RBI single, chasing Rogers from the game.
Greg Reynolds took over on the mound and Sandoval greeted him by crushing a three-run homer to right field, extending the Giants' lead to 10-1.
Colorado had two on with one out in the bottom of the fourth and a throwing error by Fontenot allowed Wigginton to score. Another runner came home on a fielder's choice.
The Giants got one of the runs back on Crawford's leadoff blast in the fifth, and the Rockies pushed across two runs in the home half on RBI hits by Wigginton and Chris Iannetta.
Beltran scored from third on an error in the sixth.
Giants closer Brian Wilson returned from the disabled list Sunday and tossed a 1-2-3 eighth, his first action since August 15 due to elbow inflammation...Rogers entered Sunday with a 9.86 ERA at home this season.