SAN DIEGO -- For the most part, Madison Bumgarner was sharp over seven frames in his first start back from the disabled list Saturday night. But it was his former batterymate who stole the show and spoiled Bumgarner's return.

Hector Sanchez, a late entry into the Padres' lineup after starting catcher Austin Hedges was scratched, launched a walk-off two-run blast off the third deck of the Western Metal Building, sending the Padres to a 5-3 victory.

"I know my job," said Sanchez, whose playing time has been limited this season. "I have to be ready every single day. I have to come to the ballpark, get ready, put myself in the situation where if something happens I have to be ready."

It was the first career walk-off homer for Sanchez, who spent five seasons with the Giants from 2011-15 -- and has tormented them ever since. He capitalized on a poorly placed fastball from Giants reliever Steven Okert for his seventh homer since joining the Padres last May. Three of those have come against San Francisco, including a game-tying blast in the ninth inning earlier this season.

Before Sanchez's heroics, Bumgarner allowed three runs on four hits, while striking out five in his first start since he injured his shoulder in a dirt-bike accident April 20. He opened the game by striking out the side, but surrendered a solo homer to Matthew Szczur in the third and a two-run shot to Jabari Blash in the fourth. The Padres didn't do much damage otherwise.

"I felt pretty good the whole time," said Bumgarner, the four-time All-Star and 2014 postseason hero. "I gradually built up to it. I was making my pitches from the first inning."

Padres starter Jhoulys Chacin withstood a rocky first couple of frames, before settling in for six innings of three-run ball. Joe Panik took Chacin deep in the sixth, tying the game at 3, but the veteran right-hander was otherwise sharp as the game progressed.

MOMENTS THAT MATTERED

Blashtoff: Blash was red-hot at Triple-A El Paso before his callup Friday night. That's carried over at the big league level. He launched a Statcast-projected 427-foot blast to straightaway center field against Bumgarner, putting the Padres on top in the fourth after their sluggish start. Blash, who is 4-for-8 with a walk since his return, also singled to spark the ninth-inning rally.

"The swing looks shorter, more compact, gets to pitches a little bit better," said Padres manager Andy Green. "He's got tremendous power. I've always wanted to see him get a consistent opportunity here, and now his swing ... warrants that kind of opportunity."

Settling down: Fifty-seven pitches into his outing, Chacin had recorded just five outs, and the Giants were threatening to blow the game open. With the bases loaded in the second, Buster Posey sent a deep fly to left, but Szczur tracked it down a couple of steps in front of the wall. It marked an early turning point, as Chacin found a bit of a groove from there.

"We're an inch away from having a six-run lead there," Giants manager Bruce Bochy said.

Chacin allowed a cue-shot double to Brandon Crawford to start the third, but held the Giants hitless otherwise over the next three frames.

"After Posey hit the fly ball in the second inning, deep to left, that's when I started thinking you have to settle down and start making good pitches," Chacin said. "That's when I turned the page."

QUOTABLE

"It's fun seeing him succeed today. He's been such a good teammate, and he's had such limited opportunity to play. … Everybody loves the energy he brings." -- Green, on Sanchez

SOUND SMART WITH YOUR FRIENDS

Sanchez's walk-off shot was his fourth homer of the season, but just his first as a member of the Padres' starting lineup. His three pinch-hit home runs are tied with Adam Lind for the most in the Majors.

HEDGES SCRATCHED

Hedges took a foul ball to the mask Friday night and was shaken up. But he was in the starting lineup until batting practice Saturday when Green said he began to feel "a little hazy." Hedges will be re-evaluated Sunday morning.

WHAT'S NEXT

Giants:Jeff Samardzija, who has done virtually everything he can to succeed yet owns a 4-10 record, will start Sunday's series finale beginning at 1:40 p.m. PT. The right-hander has sustained astounding command, striking out 127 while walking 14 in 118 innings.

Padres: After an injury-plagued first half, Trevor Cahill has finally put his shoulder and back issues behind him. He'll take the ball for Sunday's series finale with first pitch slated for 1:40 p.m. PT.

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