SAN DIEGO -- Hector Sanchez knows the drill of being a backup catcher.

"It's not an easy job," he said, "but I have to be ready every single day."

Sanchez got a rare chance to play Saturday and delivered a two-run, walk-off home run as San Diego defeated the San Francisco Giants 5-3 in left-hander Madison Bumgarner's return.

"It's fun to see him succeed because he has had such limited opportunities to play," said Padres manager Andy Green, who inserted Sanchez late into the lineup when Austin Hedges was unable to go. "You wouldn't think so by looking at his numbers, but he has won games for us, over and over.''

Of Sanchez's four home runs this year, three have been as a pinch-hitter and then there's Saturday's dramatic ninth-inning moon shot off reliever Steven Overt that was crushed 407 feet.

"Like any hitter, you are always looking for the fastball in the strike zone and then you try to put a good swing on it," said Sanchez, a former Giant. "You just want to hit a line drive and get that run in and get the 'W.' To get the victory is more important to me."

Brandon Maurer (1-4) worked the eighth and got the win, the Padres' sixth in nine games.

Cory Gearrin (3-3) faced one batter, but he absorbed the loss as Jabari Blash singled and scored the go-ahead run to send the Giants to their sixth loss in their past eight games.

Bumgarner started for the first time since injuring his left shoulder in a dirt bike accident on April 20. The left-hander began with a flourish as the Giants ace struck out the side in the first inning on his way to retiring the initial seven batters he faced.

"I felt pretty good the whole time and we kind of gradually built up to it," Bumgarner said. "We were just making pitches pretty much from the first inning on tonight.

"I knew I wasn't going to be able to get much over 100 (pitches), so yeah, if you can get out there for seven (innings), I'll take that any time."

Bumgarner, a four-time All-Star and the 2014 World Series MVP, didn't show much rust. He worked seven innings and surrendered three runs and four hits. He had five strikeouts and two walks in a 102-pitch effort.

"Nice job by Madison, it really was," Giants manager Bruce Bochy said. "It was good to have him back, his presence. He gave us a chance to win and a quality start."

Jhoulys Chacin pitched six innings, allowing three runs, six hits and four walks. He struck out four in failing to win his third straight start and to beat the Giants for the third consecutive time this season.

Joe Panik tied the score at 3 with his solo homer in the sixth inning. Chacin tried to sneak a 78 mph fastball past Panik and he nailed it for his sixth home run of the year.

Blash smacked the second of the Padres' two homers, a two-run, 424-foot shot in the fourth inning for a 3-2 lead. For Blash, who was called up from Triple-A El Paso on Friday, it was his second homer of the year and his first since April 25.

Matt Szczur's homer in the third pulled the Padres within 2-1. Szczur punished Bumgarner's elevated curveball with a 407-foot blast.

NOTES: Giants RHP Johnny Cueto was placed on the disabled list with blisters on his throwing hand. Manager Bruce Bochy is hopeful Cueto won't miss more than two starts. ... Giants LHP Madison Bumgarner (shoulder) was activated off the DL. ... RHP Matt Cain will replace Cueto in the rotation. ... Padres C Austin Hedges didn't start after being struck in the face mask by a foul tip in Friday's game. ... Padres rookie Jose Pirela made his first appearance at third base. ... Padres OF Travis Janikowski (foot) has begun his rehabilitation assignment in the Arizona Rookie League.