SAN FRANCISCO -- Wil Myers didn't look to be a likely hero after going 0-for-5. But that sixth at-bat in the 12th inning changed everything.

Myers belted his second three-run homer in two days -- this one breaking a tie -- to lead the San Diego Padres to a 5-2 comeback win over the San Francisco Giants at AT&T Park on Sunday.

"I felt good all game," Myers said. "I swung the bat real well yesterday, felt really good today. I put three good swings on balls, didn't really get anything in return, but was able to stay with it there that last at-bat and put a good swing on it."

That good swing, accounting for his seventh home run, enabled the Padres to win the weekend series after facing a 2-0 deficit in the Sunday game as late as with one out in the ninth.

That was when former Giant Hector Sanchez stroked a pinch-hit, two-run home run off San Francisco closer Mark Melancon, who was 5-for-5 in save opportunities since blowing a lead in the season opener on April 2.

"Today was on me 100 percent," Melancon said. "A cutter, down the middle, right where he was looking. You leave pitches out over the plate, that's what's going to happen."

San Diego reliever Ryan Buchter (2-1) pitched the 10th and 11th to pick up the win, and Jose Torres earned his first career save with a 1-2-3 12th.

"If we don't get our act together, it's going to get ugly," Melancon said of the 9-17 Giants. "There are too many good teams out there ready to go after us. This energy level needs to get going. We need to pick up our play, throw quality strikes, and we need to figure it out."

San Diego's Luis Sardinas reached on an error by Giants shortstop Eduardo Nunez to start the ninth before Sanchez produced his third career pinch homer, and first of the season, after Melancon struck out Hunter Renfroe.

"That was incredible, just a great at-bat," Myers said of Sanchez. "I even told (Austin) Hedges before, 'He's going to hit a home run right here.'"

In the 12th, Myers hit a 1-1 pitch off Giants reliever George Kontos after Cory Spangenberg and Erick Aybar hit soft singles to the outfield.

"For Wil, that's a huge step forward," Padres manager Andy Green said. "It wasn't a great day for him offensively. He swung the bat well early but didn't have anything to show for it. Walking through the day with an 0-fer, then steps up with a big swing late."

Kontos (0-2) said he was trying to get ball inside to Myers, but he made a mistake with his location.

"Gave up the first couple of bloop singles that just fell in front of our outfielders, and I didn't execute that pitch inside enough to him," Kontos said. "He's had a hot series. A mistake to a guy like that, he's going to put a good swing on it. He's a tough out. He definitely made me pay for it, unfortunately."

The Giants broke through with the game's first run in the fifth inning.

Joe Panik led off by getting hit by a 2-1 pitch. Gorkys Hernandez failed on a first-pitch bunt attempt, then laced an 0-2 fastball into the right field corner to give the hosts runners at second and third with no one out.

Giants starting pitcher Ty Blach fell behind at the plate 0-2 but managed to lift a sacrifice fly to medium center, and Panik scored uncontested with the throw going to third. Padres starter Clayton Richard worked out of the jam, as second baseman Yangervis Solarte dived to his left to glove Nunez's bid for a ground-ball single to right before Brandon Belt struck out.

The Giants tacked on another run in the sixth and chased Richard in the process. Hunter Pence drew a leadoff walk and moved to second on Buster Posey's excuse-me swing and groundout to third.

Michael Morse followed with a ringing double high off the right field fence to plate Pence and end Richard's outing. Lefty reliever Brad Hand induced two grounders to third to end the threat.

Blach, who was in line for the win, surrendered three hits in seven shutout innings. The left-hander finished with a flurry, retiring the last nine he faced. He worked out of a pair of two-on jams in the third and fourth innings when the game was still scoreless.

Richard was charged with two runs on six hits in 5 1/3 innings for the Padres (11-16).

NOTES: The Giants recalled veteran RHP Bryan Morris from Triple-A Sacramento before the game, and they designated RHP Neil Ramirez for assignment in a corresponding move. The 30-year-old Morris will be asked to add depth to a struggling bullpen while the Giants hope to retain Ramirez and send him to Sacramento if he goes unclaimed. Ramirez is out of options. ... An error in the second inning by Giants 2B Joe Panik, on a ground ball, was only his second in 94 chances this season. ... San Diego LHP Clayton Richard went 2-for-2 with a pair of hits that touched the right field wall, but both were only singles.