Vogelsong hopes to bounce back from another rough start Sunday when he tries to help the Giants to a fifth straight victory and first road sweep of the Arizona Diamondbacks in two years.Buster Posey hit a two-run homer and Barry Zito threw 6 2/3 strong innings for San Francisco (83-62) in Saturday's 3-2 win. Looking to match a season high with their fifth consecutive victory, the Giants also are trying for a fifth straight win at Chase Field, where they have not swept the Diamondbacks (71-74) since July 22-25, 2010.San Francisco owns a 7 1/2-game lead over Los Angeles in the West."What's been nice is guys are continuing to go out with that fire and play hard," Posey said. "Nobody's taking anything for granted."Vogelsong (12-8, 3.40 ERA), however, needs to get back on track.The right-hander is 2/3 with a 9.37 ERA in his last six starts and allowed four runs in five innings of a 6-5 loss at Colorado on Monday. That came after he was roughed up for six in 3 1/3 innings of an 8-6, 11-inning home loss to Arizona on Sept. 4."I'm costing us games right now and I'm not real happy about it," said Vogelsong, who allowed seven runs over 12 1/3 innings of the two games he's won during that stretch. "I'm just not making pitches, missing locations."Despite his recent struggles, Giants manager Bruce Bochy has not lost faith in the 2011 All-Star."He's one of our guys and he's going to be out there," Bochy said. "We have all the confidence in the world in him. He's done an unbelievable job for us this year. Vogie is going to be just fine."Despite his most recent home outing against the Diamondbacks, Vogelsong is 1-0 with a 2.08 ERA in two starts at Chase Field.Posey has batted .483 (14 for 29) with three homers and seven RBIs in his last seven games.Giants leadoff hitter Angel Pagan, who had two hits Saturday, is 8 for 17 (.471) during his team's four-game winning streak at Arizona.Posey and Pagan, however, are a combined 2 for 12 against scheduled Diamondbacks starter Patrick Corbin (5-7, 4.19).The rookie left-hander is 0-3 with a 6.00 ERA in four starts since winning at Houston on Aug. 18. He gave up three runs in 5 1/3 innings of an 8-2 loss at San Diego last Sunday.One start prior to that outing, Corbin allowed four runs and struck out six in five innings of a 9-8, 10-inning loss at San Francisco on Sept. 3. He is 1-0 with a 3.75 ERA in two starts against the Giants.Catcher Miguel Montero had two hits Saturday for Arizona, which has scored four or fewer runs in 12 straight home games to match a franchise record."We had a couple of chances with runners in scoring position and we scored only four runs in two nights," said manager Kirk Gibson, whose team has stranded 21 runners in the first two games of the set.Montero has hit .396 (21 for 53) in his last 14 games, and .435 (10 for 23) in his last six against the Giants.