SAN DIEGO -- One team was fighting for a postseason spot. The other was just fighting.

Jedd Gyorko's two-out RBI single off Santiago Casilla in the ninth inning lifted the San Diego Padres to a 5-4 win over the Giants on Wednesday night, dealing a serious blow to San Francisco's playoff hopes.

Gyorko drove in right fielder Matt Kemp, who hit a one-out double off George Kontos (4-3).

"A lot of emotions in this game with back and forth, happy to come out on top," Padres interim manager Pat Murphy said.

The defending World Series champion Giants fell seven games behind the first-place Los Angeles Dodgers in the National League West with 11 games remaining. San Francisco trails the Chicago Cubs by 9 1/2 games for the second NL wild card after its bullpen squandered leads of 2-0 and 3-2 in the seventh and eighth innings, respectively.

"Hanging by a thread," Giants manager Bruce Bochy said. "This was a tough one to let get away. But we're still breathing, and that is the way you look at it, and we will keep saying, 'You never know,' and keep going out there and playing hard."

The Giants tied the score in the ninth off Craig Kimbrel (3-2). First baseman Buster Posey reached on an error by Kemp and advanced to third on shortstop Brandon Crawford's double. Pinch hitter Mac Williamson and second baseman Kelby Tomlinson struck out, but Kimbrel unleashed a wild pitch to score Posey.

"We got a break there with the wild pitch, but unfortunately we couldn't take advantage of it," Bochy said.

Kemp said Posey's lost the fly ball in the lights.

"I tried my best to stay in there as long as I could, but unfortunately it hit my glove and I didn't make the play," Kemp said.

In the bottom of the eighth, Padres rookie center fielder Travis Jankowski laced an opposite field double off Sergio Romo to score first baseman Brett Wallace and second baseman Gyorko, giving San Diego a 4-3 lead.

San Francisco rookie right fielder Jarrett Parker stroked his second career homer off reliever Joaquin Benoit in the top of the eighth to give the Giants a 3-2 advantage.

However, the Giants couldn't hold back the Padres, who won for just the fourth time in 12 games.

Jake Peavy blanked the Padres for six innings before San Diego rallied against the Giants' relief corps.

"Our bullpen has been tough all year," Peavy said. "This was just a tough night, and we just couldn't finish the deal there a few times."

In the seventh, San Diego third baseman Yangervis Solarte tied the game with a two-out, two-run double off Josh Osich. Gyorko singled and catcher Derek Norris walked before Solarte hit his second double of the game.

Padres starter Andrew Cashner lasted six innings, allowing two runs and two hits while matching a career high with five walks. He had six strikeouts.

Crawford's two-out, two-run single in the first inning gave the Giants a 2-0 lead. He drove in center fielder Angel Pagan and left fielder Alejandro De Aza after they walked.

The Giants trudged out of the clubhouse knowing the end could be near.

"I'm not going to sit here and tell you I feel great about our chances," Peavy said. "That being said, we're not eliminated, and we've needed them all for a while now.

"When you lose one like this, it is tough, and staring at those numbers in the face, it is harsh reality. But we are going to show up tomorrow and see if we can win and go see if we can't sweep Oakland and go sweep the Dodgers and win out."

NOTES: Padres TV announcer Dick Enberg announced his retirement after the 2016 season, which will be his 60th in sports broadcasting. This summer he received the Baseball Hall of Fame's Frick Award for broadcasting excellence. ... San Diego CF Wil Myers (wrist) was scratched from the lineup. ... Padres INF Brett Wallace started at first base Wednesday, one night after belting his major-league-high fourth pinch-hit home run. ... San Diego RHP Shawn Kelley (forearm) was fine after pitching Tuesday for the first time since Sept. 1. ... Buster Posey was back in the Giants' lineup at first base after sitting out Tuesday due to sore hip. ... The Giants selected the contract of INF/OF Kevin Frandsen from Triple-A Sacramento. He opened his major league career with San Francisco, playing with the Giants from 2006-08. ... San Francisco placed INF Juan Perez (oblique) on the 60-day disabled list, clearing a spot for Frandsen on the 40-man roster.