Padres starter Ian Kennedy (4-6), who entered the game with a 10-4 record and a 2.42 ERA lifetime against the Giants, retired the first six batters he faced before San Francisco amassed five runs in the third inning. Posey's fourth career grand slam was a towering fly into the left-field seats on a 2-2 changeup. Posey is 3-for-6 with 10 RBIs with the bases loaded this season and owns a lifetime .400 average (16-for-40) against Kennedy.
"I was just trying to stay short with my swing and hit a line drive somewhere," Posey said. "Fortunately, it turned into something more."
Vogelsong (6-5) surrendered five hits in six shutout innings. The right-hander held San Diego hitless in five at-bats with runners in scoring position and the Giants recorded their Major League-leading 12th shutout. That total includes four against the Padres.
MOMENTS THAT MATTERED Cream rises to top: San Francisco's seventh and eighth hitters were extremely productive. Andrew Susac reached on an error that could have been ruled a hit to open the third inning, then scored the Giants' first run on Joe Panik's sacrifice fly. Gregor Blanco walked and scored on Posey's grand slam. One inning later, Susac tripled and came home on Blanco's single. More >
"You can't give them five outs. I thought we gave them extra outs there. You've got to make the play on defense early, and that changes things significantly," said Padres interim manager Pat Murphy of the Will Middlebrooks error on the Susac ball to start the inning.
Rally killer: A half-inning after Posey's grand slam, the Padres looked like they were set to get some runs back when Yonder Alonso walked and Justin Upton doubled to put runners on second and third with no outs in the fourth inning. But a rundown, a strikeout and a ground ball ended their threat.
"Most times in that situation, you try to minimize the damage," Vogelsong said. "But I really felt like there, to keep momentum on our side, I had to try to keep them at zero."
Happy returns: New Padres reliever Marcos Mateo, recalled earlier in the day from Triple-A El Paso, made his first big league appearance since July 4, 2011, while with the Cubs. Mateo struck out Brandon Crawford and Matt Duffy, allowed an infield single to Angel Pagan and got Posey to ground out to end the inning.
"I was really excited for him," Murphy said. "That was a bright spot on a blah day."
Hitless at the top: San Diego right fielder Matt Kemp, batting leadoff for the first time since 2010, when he was with the Dodgers, went 0-for-4. Kemp is the seventh player to bat leadoff for the Padres this season. More >
"I've been told by the staff that this has kind of been the microcosm of the season." -- Murphy on the loss, which came on the heels of a big win Tuesday, 3-2, when the Padres chased Madison Bumgarner
SOUND SMART WITH YOUR FRIENDS
The Padres have been blanked 11 times this season, four times by the Giants.
WHAT'S NEXT Padres:James Shields (7-1, 3.75) gets the start Thursday in the 12:45 p.m. PT series finale against the Giants. This will be his second start against the Giants this season. He got the win on April 11, allowing one run over seven innings in a start at Petco Park.
Giants:Chris Heston, Thursday's starter for San Francisco, will try avoid the fate that befell him when he last faced San Diego at AT&T Park on May 6. He yielded five runs and 11 hits in five innings as the Padres triumphed, 9-1.