Colorado, which made an impressive late-season charge to win the NL West last season, pulled within six games of first-place Arizona and is only three games behind Los Angeles for second place. It's the closest the Rockies have been to the Diamondbacks since July 28.
De La Rosa (7-7) allowed two runs and five hits to win for the fourth time in his last six decisions. The left-hander struggled with his command but got plenty of help from Colorado's defense and some timely hitting from his teammates to lead the surging Rockies to their ninth win in their last 11 games.
Brad Hawpe added two hits and scored three times while Troy Tulowitzki had two RBIs for Colorado, which handed San Francisco its second straight loss.
The Rockies scored four runs in the third off Matt Palmer (0-2), who was making only his third career start. Atkins and Ianetta both delivered two-run singles in the inning when Colorado batted around to break the game open.
Tulowitzki's sacrifice fly in the fifth made it 5-2 and the Rockies added two more runs in the seventh off Giants' reliever Jack Taschner.
Palmer, who was called up from the minors on Aug. 14, lasted only 4 1-3 innings and gave up five runs with six walks.
Rich Aurilia had three hits and scored both runs for the Giants, who had won five straight and eight of 10 before dropping the first two games of their series with Colorado.
De La Rosa rebounded from a loss in his last start to complete what has been a stellar month for the lefty. In six games during August, including two relief appearances, De La Rosa is 2-1 with a 2.22 ERA.
Jason Grilli pitched three perfect innings of relief to earn his first career save.
The Rockies needed the strong outing from their starter after placing closer Brian Fuentes on the bereavement list earlier in the day. Fuentes notched his 26th save against the Giants on Monday but left the team to be with his family.
Fuentes can stay on the bereavement list three to seven days but Rockies manager Clint Hurdle is not putting a timetable on Fuentes' return.
"When it's family issues I don't push it," Hurdle said. "He just needs to get back to his family and he'll come back when he can."
Right-hander Manuel Corpas, who has four saves in 11 tries, will handle the closing duties for the Rockies until Fuentes returns.
Notes:@The Rockies called up RHP Steven Register from the minors to take Fuentes' roster spot. Register was 5-3 with 16 saves and a 3.32 ERA for Triple-A Colorado Springs. ... Colorado rookie 3B Ian Stewart singled in the seventh to extend his career-high hitting streak to 10 games. ... The Rockies left the bases loaded three times, and left two runners on in two other innings.