Less than an hour before first pitch on Monday, the Giants scratched Mike Yastrzemski from their starting lineup with left hand soreness, an aftereffect of the hit-by-pitch he sustained on the final day of Spring Training last week.

But Yastrzemski still managed to show why he’s the Giants’ most valuable player, coming off the bench to drill a pinch-hit, go-ahead home run to lift his club to a 3-2 series-opening win over the Padres at Petco Park.

With the game tied, 2-2, in the top of the seventh, Yastrzemski crushed a 2-0 sinker from Padres right-hander Craig Stammen out to center field for his first home run of the season and the second pinch-hit homer of his career.

“I’m used to seeing great swings from him, so that didn’t surprise me, but it was certainly a gutsy moment for him,” manager Gabe Kapler said. “He’s a resilient kid and did a nice job in that plate appearance.”

All three of the Giants’ runs came via solo shots, as Darin Ruf and Evan Longoria also went deep to back a strong outing from right-hander Anthony DeSclafani, who fired five innings of one-run ball in his Giants debut. San Francisco now has nine home runs through its first four games, tied with the Astros for the most in the Majors.

The Padres threatened in the bottom of the ninth, putting runners on first and second with two outs after Manny Machado walked and Eric Hosmer was hit by a pitch, but closer Jake McGee induced a flyout from Tommy Pham to end the game.

Yastrzemski, 30, blossomed into a star for the Giants in 2020, when he placed eighth in National League MVP voting after hitting .297 with a .968 OPS and 10 home runs over 54 games. He escaped serious injury after being struck on the left hand by a pitch from left-hander Sean Manaea in the Giants’ spring finale, but he didn’t look entirely like himself over the club’s opening series in Seattle, going only 1-for-13 with six strikeouts over three games.

Yastrzemski was blunt in assessing his performance afterward and deflected when asked if his hand was affecting him at the plate.

“There’s no excuse,” Yastrzemski said Saturday. “I just stunk this weekend.”

Before batting practice at Petco Park on Monday, though, Yastrzemski experienced swelling in his left hand after going through his outfield throwing drills, prompting the Giants to remove him from the lineup. Still, Yastrzemski demonstrated that he was pain-free while swinging the bat and told Kapler that he’d be available for a pinch-hit appearance if needed.

That opportunity presented itself when the pitcher’s spot came up in the seventh against Stammen, who threw a low-and-away sinker that Yastrzemski drove out for a 406-foot blast.

“I knew I hit it good,” Yastrzemski said. “I wasn’t sure if it was gone for sure. I was obviously hoping it was either a home run or a deep flyout. It was kind of working into what I wanted to do mentally with my swing. I was getting beat a lot in Seattle and spinning off the ball. I just wanted to really stay through the middle of the field, and I just got a pitch that I could do it with.”

As an everyday player for the Giants, Yastrzemski doesn’t have a ton of experience pinch-hitting in the Majors, but he said he learned a lot from watching former teammate Pablo Sandoval, who excelled in a bench role at the tail end of his tenure in San Francisco.

“I just watched him when he was getting ready for his at-bat,” Yastrzemski said. “Everybody knows him as this fun-loving guy, and the second that he knew there was a pinch-hit opportunity, he was quiet, about his business, made sure that he was completely mentally checked in and ready to take his at-bat. Just being able to observe him and see how he prepared, what his mentality was and what his routine was is what has really helped me and in those situations.”

Two of the Giants’ nine home runs have come from pinch-hitters, an indication of the weapons Kapler expects to have off the bench as his club returns to the traditional National League style of play this year.

“We’ve got a ton of talent on our bench, which not too many teams are lucky to have,” Yastrzemski said. “I think it’s a weapon, to be able to have the confidence in these guys to come off the bench and put together good at-bats in tough situations. Obviously, it’s a hard thing to do and you never really expect anything of anyone who’s pinch-hitting. You just hope for the best.”

Now the Giants will do the same with Yastrzemski’s hand, which he said is feeling better. He is expected to be reevaluated before Tuesday night’s game to see if he’ll be ready to play the field and return to the starting lineup against Padres right-hander Yu Darvish.

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