If the Giants can win the series finale, they'll leave town with their largest lead in four weeks.San Francisco seeks its first three-game sweep at Dodger Stadium in five years Wednesday night.The Giants (68-55) stole the Dodgers' one-half game division lead with a 2-1 victory in Monday's series opener, then won 4-1 on Tuesday night to take a 1 1/2-game advantage over their rivals.Buster Posey, who started at first base for the Giants while Hector Sanchez took his usual spot behind the plate, opened the scoring Tuesday with a two-run single in the first inning. San Francisco added two more in the fourth on a RBI single by Brandon Crawford and a double by Angel Pagan.Pagan, who had three hits and threw out a runner at the plate, is batting .478 with three doubles during a five-game hitting streak.The Giants, who last swept a three-game series at Chavez Ravine from April 24-26, 2007, are exacting some revenge after the Dodgers (67-57) swept three games in San Francisco at the end of July to create a virtual tie atop the West. Now, San Francisco can secure its largest lead since it was 2 1/2 games up July 25.All the Giants need for that to happen is another win from Matt Cain (12-5, 2.90 ERA).Cain has allowed three runs over 15 1/3 innings to win his last two starts after going 0-2 with a 5.26 ERA in his previous four. He permitted one run and four hits while striking out six and walking none in eight innings of a 10-1 rout at San Diego on Friday."He's tough when he's on," Giants manager Bruce Bochy said, "and he was on (Friday)."Cain is especially tough when he gets some run support.Since 2010, Cain is 31-1 with a 2.54 ERA in the 45 games he has received at least three runs of support, with San Francisco winning 40 times.Cain allowed three runs and nine hits in seven innings against the Dodgers on July 27, when the Giants lost 5-3 in 10 innings at home.Los Angeles outfielder Andre Ethier is mired in an 0-for-16 slump, but is batting .480 in 50 career at-bats against Cain -- his highest average against any pitcher he has faced at least 17 times.Teammate Matt Kemp -- 1 for 20 in his last six games -- may not be as excited to face Cain considering he's 2 for 16 in their matchups since 2010.The Giants have won four of six since Melky Cabrera's drug-related suspension, but they may face a tough challenge Wednesday against Los Angeles starter Chris Capuano (11-8, 3.14).Capuano has a 2.01 ERA in three starts this month, striking out 24 and walking five in 22 1/3 innings. He gave up three runs -- two after he had departed -- and five hits in 7 1/3 innings of a 4-3, 11-inning loss against Atlanta on Friday.Capuano has also been sharp in his 12 starts at Dodger Stadium, posting a 2.17 ERA -- the NL's third-best home mark. Unfortunately for the left-hander, Los Angeles has supported him with two runs or fewer in eight of those contests, leaving him with a 5-4 record.This will be Capuano's first taste of the Dodgers' rivalry with the Giants after going 0-2 with a 2.92 ERA in two starts against them last year with the New York Mets.