SEATTLE -- When Ryan Vogelsong takes the mound, one of his goals is to try and match what teammate Matt Cain did before him in San Francisco's rotation.

Good luck trying to match a perfect game.

"I told him before the game that I'm trying to keep up with him and he's making it tough. He's not making it easy," Vogelsong said.

Helped by homers from Buster Posey and National League hitting leader Melky Cabrera, Vogelsong won his sixth straight decision on Friday night, and the Giants opened a three-game interleague series with a 4-2 win over the slumping Seattle Mariners.

Posey led off the second inning with a solo home run into the second deck of the left field seats, and Cabrera added a two-run shot in the eighth inning that proved to be more important than it first appeared. The Giants have now clubbed eight homers in their past four games, although this is unlikely to be a continued run of slugging from a team not known for its power hitting.

Posey turned on a hanging offspeed pitch from Seattle starter Jason Vargas (7-6) for his eighth homer of the season, a 386-foot shot that landed in the first row of seats in the second deck above the Giants bullpen. Cabrera's sixth homer of the season didn't have the majestic arc of Posey's, but cleared the fence in left-center field by about a foot as Franklin Gutierrez was unable to chase it down.

"I think they just seem to come in bunches. It's just the way that it goes," Posey said.

Few will ever match what Cain did with his 14 strikeouts in throwing the 22nd perfect game in baseball history on Wednesday against Houston. But to a lesser extent, Vogelsong was awfully good on Friday night even when he didn't have his best stuff.

Vogelsong took a shutout into the seventh inning and allowed just two hits before surrendering a pair of singles to Dustin Ackley and Miguel Olivo to begin the eighth. Before that, Vogelsong had retired 11 straight and given up just a pair of doubles to Jesus Montero and Olivo earlier in the game.

More importantly, the past eight times Vogelsong has gone to the mound, the Giants have come away with victories. Vogelsong is now 5-0 in his past seven road starts and only once in his past nine starts has he given up more than two earned runs.

His last loss came on May 3 against Miami.

"What you like about him is he keeps his composure out there, even with the walks, he continues to grind it out and make pitches," Giants manager Bruce Bochy said.

Vogelsong struck out six and walked three. He left after giving up a pair of hits to Dustin Ackley and Olivo to start the eighth, snapping a streak of 11 straight batters retired. Reliever Javier Lopez was greeted by a single from pinch-hitter Casper Wells to load the bases. Ichiro Suzuki hit a grounder that bounced off Lopez's glove and to shortstop Joaquin Arias, who got a force out at second base, but Ackley scored on the play. Lopez was replaced by Sergio Romo, who got Franklin Gutierrez to ground out to Pablo Sandoval at third on a ball that probably should have been a double play and allowed Olivo to score. Romo then got Kyle Seager to ground out to end the rally.

Santiago Casilla pitched the ninth for his 18th save in 19 chances.

"I said to these guys last year I didn't want to be the weak link in the rotation," Vogelsong said. "I'm just trying to go out there and feed off of them."

Joaquin Arias drove in San Francisco's other run with a sacrifice fly in the fourth that scored Angel Pagan. But there were plenty of other chances for the Giants, who hammered Vargas for 10 hits. It was the most hits allowed this season by Vargas, who had allowed nine hits in his previous two starts. Vargas has lost his past two starts.

"He kept us in it. We're struggling on offense here right now, but he deserved to be out there late," Seattle manager Eric Wedge said of Vargas. "He was doing a good job controlling the game."

Game notes
Giants' RHP Tim Lincecum, who grew up in the Seattle suburbs and was a star in college at Washington, will take the Safeco Field mound for the first time on Saturday night trying to stop a personal five-game losing streak. Lincecum has not won since April 28. ... Seattle dropped Ackley to seventh in the batting order for the first time this season. Wedge said he wanted to balance the top of his order and not be so left-handed hitting heavy. ... Giants' 1B Brandon Belt saw his consecutive games with a homer streak end at three.