SAN FRANCISCO -- The tradition began a couple of years ago at Triple-A Sacramento, when former Giants farmhand Zach Green decided to grow a mustache for the month of May.

As Austin Slater tells it, Green subsequently “went absolutely bananas” at the plate, inspiring several of his River Cats teammates to copy his new look. Mike Yastrzemski was an early adopter, with Slater eventually following suit toward the end of the month.

“Slowly everyone that started doing it just started raking,” Slater said. “I jumped in for like the last week or week and a half and got hot myself.”

When he found himself mired in an early slump to start the 2021 season, Slater decided it was time to change things up. He and Yastrzemski agreed to bring back Mustache May, a move that appears to already be paying dividends for the Giants.

Sporting his fresh ‘stache, Slater crushed a game-winning home run to the opposite field to lift the Giants to a 5-4 win over the Padres on Friday night at Oracle Park. Slater entered Friday with only three hits in his previous 26 at-bats (spanning 11 games), but he drove a 2-1 fastball from San Diego right-hander Keone Kela into the arcade in right field in the seventh inning to help San Francisco retain its hold of first place in the National League West.

“I needed to switch something up,” Slater said afterward. “I was going through a little skid there. Sometimes it’s funny things like that. We’ll see if it keeps going, but it’s off to a good start.”

Slater stayed hot in Saturday's 7-1 victory, entering as a pinch-hitter in the sixth inning. He padded the Giants' lead with an RBI single in the sixth, and he crushed a 456-foot two-run homer to straightaway center field in the eighth. Yastrzemski went 0-for-4 but drew a walk.

Asked to grade his outfielders’ mustaches on the 20-80 scouting scale, manager Gabe Kapler gave Slater a 65 ‘stache but said he wasn’t a huge fan of the flavor saver that Yastrzemski has maintained.

“If Yaz would just shave this little thing below his lip, I think that would pop him into the 80 range,” Kapler said.

Yastrzemski’s response?

“My feelings were a little hurt,” Yastrzemski said. “Everybody’s got to have a little personal flair. Kap is a players’ manager. He likes us to be ourselves, and to be docked for having my own take on it hurts a little bit. We’ll put some consideration into it, but I have to separate myself from Slater a little bit. We can’t have the exact same mustache. Hopefully we’ll get a couple more guys on board and we’ll see what happens here in the next couple weeks.”

One of those players appears to be young Mauricio Dubón, who is still working on his ‘stache game.

“I don’t want to blow up his spot,” Slater said, “but I think he’s trying.”

Yastrzemski, who returned to the starting lineup on Saturday for the first time since coming off the injured list, said there are no plans to keep the ‘staches beyond May, as he and Slater don’t want to push their luck and spoil the vibes.

“It’s strictly a May thing,” Yastrzemski said. “You can’t overwork it. You can’t abuse it. It’s here for the month of May and that’s it, no matter how it goes.”

Sanchez to IL, Gausman returns
Before Saturday’s win over the Padres, the Giants activated Kevin Gausman and placed Aaron Sanchez on the injured list with right biceps tightness.

Kapler said Sanchez had been dealing with the issue for his past couple of starts and believes the break will allow the 28-year-old right-hander to get his arm back to full strength.

Sanchez, who signed with the Giants on a one-year, $4 million in February, logged a 3.18 ERA over his first six starts, but he’s averaging 89.6 mph on his four-seam fastball, down from 93.4 mph in 2019. The Barstow, Calif., native missed the entire ‘20 season while rehabbing from right shoulder surgery.

“I know Aaron believes in himself,” Kapler said. “We all believe in Aaron. We know there is a version of him in there that is competitive like he was for us in every start and getting outs like he did often for us. And also one that can maintain and hold his stuff deeper into games and one who has some kind of high-octane stuff to go along with his athleticism. We feel like there’s a chance that some of that gets to his level of satisfaction, our level of satisfaction, with a little bit of a blow here.”

Sanchez’s injury means the Giants will be able to keep Logan Webb in the starting rotation once Johnny Cueto returns from the IL on Sunday. Alex Wood and Webb are slated to start the club’s two games against the Rangers next week at Oracle Park in that order.

Gausman was placed on the IL with vaccine side effects on Tuesday, but he recovered in time to take his next scheduled turn in the rotation against the Padres on Saturday, fanning seven in six innings of one-run ball.