This same line of thinking didn't help Ryan Vogelsong in the Giants' series opener, though.Bumgarner hopes to avoid losing his fourth straight start and help NL West-leading San Francisco even up its series with the last-place Rockies on Tuesday night at Coors Field.The Giants' division lead was trimmed to five games over idle Los Angeles with a 6-5 loss to Colorado (57-83) on Monday, just their fourth defeat in 12 meetings this year. Buster Posey and Hunter Pence each homered in helping San Francisco (79-62) reach the five-run mark, which is usually enough for a win, but Vogelsong again struggled."We've just got to put this one behind us," Bruce Bochy said after the Giants fell to 24-3 when scoring at least five runs since the All-Star break. "You like having a five-game lead because it does give you a margin of error. But you don't want to slide in the back door. We need to win ballgames."Vogelsong allowed four runs in five innings, and now has a 9.57 ERA in his last six starts. He came into the game 5-0 with a 1.80 ERA in six starts versus Colorado with the Giants.Bumgarner (14-10, 3.15 ERA) has enjoyed similar success against the Rockies, but also like Vogelsong, he's been struggling lately.Bumgarner, who's making his third start in the season series, has posted a 0.66 ERA in winning his last four against the Rockies, and has yielded two runs or fewer in each of his last seven starts against them. He's allowed one run in each of his last three starts at Coors Field, winning each.Colorado's Carlos Gonzalez, who is 1 for 16 in his last five games, has had some success against Bumgarner, though, batting .368 with two homers and two doubles in 19 career at-bats.While Bumgarner has routinely shut down the Rockies, little has come easy for the left-hander lately. He has a 6.48 ERA in losing his last three starts after sporting a 1.93 ERA in his previous eight. Against Arizona on Wednesday, he permitted four runs and seven hits in 6 1/3 innings of a 6-2 defeat.Colorado counters with Jhoulys Chacin (2-5, 4.50), who has allowed one run in each of his four starts after a 3 1/2-month stint with right shoulder inflammation, but wasn't particularly sharp in his latest outing.In Atlanta on Thursday, he gave up seven hits and three walks and was done after 3 1/3 innings in a 1-0 loss. The lone run scored in the second inning, when Chacin dropped the ball when his catcher threw it back between pitches and Juan Francisco alertly scored from third with a headfirst slide.The right-hander made his season debut against the Giants on April 9, allowing four runs in four innings of a 7-0 loss. He's got a 5.40 ERA in losing his last three starts in the series, and hasn't had much luck containing Pablo Sandoval, who is 7 for 14 with two homers, a double and a triple in their matchups.Chacin will also have to be careful facing Posey, who is 2 for 4 against him, and 7 for 12 with two homers and four RBIs in his last three games. The All-Star catcher is batting .538 with four home runs and 12 RBIs in his last seven games versus Colorado.