SAN DIEGO -- Hector Sanchez spent nine years in the San Francisco Giants' system, including parts of five seasons with the parent club as the catching backup to perennial All-Star Buster Posey.

"I owe the Giants a lot," the 27-year-old said Sunday.

Well, he has a strange way of showing it.

Sanchez rocketed a three-run homer off Jeff Samardzija in the bottom of the first inning Sunday to propel the Padres to a 7-1 victory over the Giants in the rubber match of a three-game series at Petco Park.

The 421-foot rocket to right on a one-ball changeup came 12 1/2 hours after Sanchez broke up a 3-3 tie with a two-run, walk-off homer in the bottom of the ninth inning. That blast landed on the third balcony of the Western Metal Supply Co. building.

"It's kind of fun," Sanchez said of his back-to-back decisive blasts. "I like the opportunity. I'm just trying to do my best."

His best comes out against his former team. Since he departed the Bay Area, Sanchez is 8-for-16 against the Giants with four homers and 11 RBIs. Three of his five homers this season have come against San Francisco -- the first of which tied a game the Padres eventually won, and the last two qualifying as game-winners.

Sanchez, who started the past two games because Austin Hedges was woozy after taking a foul tip off the mask Friday night, is 4-for-11 with three homers and eight RBIs against the Giants this season. Against anyone else, he is 5-for-35 with two homers and five RBIs.

When asked what he liked about Sanchez's at-bats the last two games against the Giants, Padres manager Andy Green replied: "Home runs."

Sanchez was far from the Padres' only standout Sunday as they ran their record to 14-5 against San Francisco after losing the first nine meetings with the Giants to start the 2016 season.

Cory Spangenberg also hit a three-run homer in the third inning off Samardzija (4-11). The Giants right-hander was ahead 0-and-2 in the count after Spangenberg fouled off the previous pitch on a safety squeeze. Spangenberg then drove a fastball 410 feet, easily clearing the fence in straightaway center.

"This has got to stop," Giants manager Bruce Bochy said of opposing teams' success on 0-and-2 pitches. "I don't know if I need to pitch out every time on 0-and-2 or what. This is happening too many times.

"They're trying to get one run in and get away with getting a three-run homer after that failed. It seems like the more we make it an issue, the more mistakes we make. We've talked about it. We've done fines. I'm sure it is a pitch he'd like to have back."

Samardzija said of his 0-and-2 mistake, "I watched Spangenberg chase a bunch of balls up in the series, so I was going for the strikeout there just because you know, one out, you can try to go for the double play. But I thought if I can get the strikeout there ... that's a frustrating pitch. ... Get it up another six inches and it's an out."

Samardzija finished strong. After Spangenberg's homer, he retired 10 of the last 11 Padres he faced, but the score was already 7-1. He wound up charged with seven runs on nine hits and no walks in six innings. Samardzija struck out eight.

Padres starter Trevor Cahill (4-3) held the Giants to one run on eight hits and a walk over 6 2/3 innings. He also fanned eight.

"My stuff stayed the same throughout the game," Cahill said. "My last pitch was as good as my first pitch. Getting the four-run lead in the first was huge. And they were aggressive, I didn't have many deep counts."

The Padres scored four in the first against Samardzija, who entered the game with a 2.04 career ERA at Petco Park.

With one out, Samardzija hit Carlos Asuaje with a pitch. Wil Myers followed with a single, ending a 2-for-14 slump. Sanchez then drove the second pitch he saw from Samardzija into the right field seats. After Samardzija struck out Jabari Blash, Spangenberg tripled to right-center and scored on Erick Aybar's single into the right field corner.

The Giants pulled to within 4-1 when Posey and Brandon Crawford opened the top of the second with back-to-back doubles. However, Cahill avoided further damage in the inning by striking out Nick Hundley and Joe Panik before retiring Samardzija on a comebacker.

Myers and Sanchez opened the Padres' third with back-to-back singles. After Samardzija again struck out Blash, Spangenberg connected on his sixth homer of the season to make it 7-1.

NOTES: Giants 1B Brandon Belt was a late scratch from the lineup due to a sprained left wrist. Belt injured the wrist Saturday night on a checked swing. He is listed as day-to-day. Buster Posey moved to first base Sunday, and Nick Hundley caught. ... Padres C Austin Hedges missed a second consecutive game after taking a foul tip on the face of his mask Friday night. Padres manager Andy Green said team doctors described the injury as "sub-concussive" and said he expects Hedges to be back in the lineup Monday as San Diego opens a three-game series in Colorado. ... The Giants return home to face the Cleveland Indians on Monday.