SAN FRANCISCO >> Wilmer Flores believed he had more game to give. His track record provided him with confidence that he could rebound from the worst season of his career, one plagued by a knee issue that never went away — ended his season. The Giants believed, too. Time and time again, Flores rewarded their faith.

He rewarded that faith on Opening Day in Cincinnati when he hit a go-ahead, three-run homer in the ninth inning.

He rewarded that faith by hitting a walk-off single against the Seattle Mariners.

He rewarded that faith by becoming one of the best hitters in baseball with runners in scoring position.

And on Friday night at Oracle Park, Flores, again rewarded their faith with the best game in his 13-year career.

He sent three home runs into the left-field bleachers — a grand slam among them — achieving the feat for the first time in his career and becoming the first Giants right-handed hitter to pull off the trifecta in Oracle Park history. With those three swings, he drove in a career-high eight runs and tied Aaron Judge for the most RBIs (41) in all of baseball, single-handedly carrying the Giants to a 9-1 win over the Athletics in their return to the Bay Area.

“I’m so happy for him,” said starter Logan Webb, who allowed one run over season-high eight innings. “Dealing with injuries last year and coming back this year, he’s a huge part of our team. We missed him last year a lot. Seeing him healthy this year and back to doing what Wilmer does is really cool.”

Added manager Bob Melvin: “I don’t know that anybody would predicted this, but when he came back in spring training and you saw that it was pretty normal to what we’ve seen before, we felt good about him. But I don’t think anybody could’ve predicted this.”

The Giants gave Flores their vote of confidence multiple times this past offseason, hypothesizing that a healthy Flores could return to his 2023 form. That proposition was far from guaranteed.

Flores sustained a knee injury earlier last year and tried to play through the pain. The result was a .206 batting average, .595 OPS and four home runs, all of which were the worst marks since he became a full-time player. On his 33rd birthday, he underwent a season-ending Tenex procedure on his right knee.

Nine months later, he’s one of their most valuable players — value that can’t be fully captured in WAR. Most of that value derives from his at-bats when runs are on the line.

Flores, with a grand slam in the third and three-run homer in the sixth, now owns a slash line of .381/.469/.667 with runners in scoring position. His 1.136 OPS in these situations is the sixth-best mark in all of baseball, well above his overall mark of .786. To outfielder Mike Yastrzemski, who has played with Flores for the last six years, that proficiency with men derives from his experience.

“You see the trends of trying to bring up guys when they’re so young and replace a lot of older players. I think that Wilmer is showing what a true veteran should be doing, and it’s really impressive. It’s incredible. He’s been in every situation that there has been in the game, basically. You see it in his at-bats. They’re consistent. They’re always really calm. He knows what he has to do, and he never tries to do too much.”

To Yastrzemski’s point, Flores said that he wasn’t trying to homer in any of his three at-bats that yielded one.

Flores stepped into the batter’s box in the third with an opportunity to break a scoreless tie: bases loaded, no outs. Flores got ahead in the count, 2-1, against the Athletics’ JP Sears before fouling off five consecutive pitches. He ran the count full on the ninth pitch, then capped off a 10-pitch battle by sneaking a middle-middle fastball over the left-field fence to give the Giants a 4-0 lead.

In the sixth, Flores strolled to the plate with runners on first and second with one out — another opportunity with runners in scoring position. The Athletics’ Michel Otañez left a four-seam fastball over the heart of the plate and sent it towards those same left-field bleachers. Left fielder Tyler Soderstrom leapt and extended his arm, but Flores’ drive had just enough juice to extend San Francisco’s lead to 7-0.

Flores’ final plate appearance of the evening featured empty bases. He’d hit two homers on nine other occasions up to that point, and Anthony Maldonado left him a fastball over the heart of the plate, he finally completed the trifecta.

“Everybody loves Wilmer here,” Melvin said. “Everybody around the league loves Wilmer. He’s about as respected as a guy as you’re going to come across. So, it’s great to have someone have a game like that. It’s doubly good that it’s Wilmer, and I think everybody really embraces him. He’s a leader.”