In a nine-round bout that initially featured evasion from atop the mound and around the field, the Padres landed the first punch at AT&T Park. An offense that had struggled to hit its weight, up and down the lineup, socked its opponent in the gut.

San Francisco counter-punched, popping San Diego in the mouth.

The Padres had a counter to the counter. His name was Rene Rivera.

The final scorecard Monday showed a 6-4 victory over the division-leading Giants, noteworthy as much for the method as for the upset. The Padres did not scratch their runs across, as they have had to do this season. Instead, they relied on a few crunching blows to left. Rivera, of all the unlikely candidates, was the hammer. The seventh batter in the order drove in five San Diego runs, setting both a career-high and a season-best for the Padres.

“We needed a game like that from one of our guys,” Padres manager Bud Black said. “It’s been a long time coming. ... You never know who’s gonna be the guy on a certain night, and tonight it came from Rene Rivera.”

The 30-year-old catcher had journeyed far and wide before arriving last year in San Diego. Though he wields an unremarkable bat, Rivera has latched on as a pitcher whisperer and a master framer of the fringe strike.

Monday, there was nothing soft-spoken or subtle about his game, unleashed in the most unexpected of flurries. After popping out in his first at-bat, Rivera came to the plate in the fourth of a scoreless game, runners on first and second. In his circuitous career, he had never faced Madison Bumgarner before Monday. The Giants’ left-handed ace opened the second at-bat with a slider.

“I was watching videos of him,” Rivera said of Bumgarner. “(Padres hitting coach) Phil Plantier had a lot of stuff on him. I just wanted to see the ball and hit it. Basically, keep it real simple.”

Rivera swung at that first pitch. A double shot down the left-field line, scoring Tommy Medica and Alexi Amarista. Though the Padres would later strand a pair of runners in the inning, the 2-0 lead still qualified as a minor coup. San Diego had come in averaging less than 2.7 runs per game.