SAN FRANCISCO -- When the Giants handed the ball to Kevin Gausman on Opening Day, they formally acknowledged Gausman’s status as the ace of the pitching staff. He’s certainly living up to that label.

Gausman matched his career high with 11 strikeouts en route to eight innings of one-run ball, but the Giants wasted his gem after rookie Gregory Santos surrendered a tie-breaking, two-run home run to Jesús Aguilar in the ninth that lifted the Marlins to a 5-2 win on Saturday night at Oracle Park.

Gausman allowed only two hits and departed after throwing 101 pitches in his longest outing since 2018, but he and the Giants came away empty-handed after Miami staged a four-run rally in the ninth. With setup man Tyler Rogers and closer Jake McGee unavailable after pitching back-to-back nights, manager Gabe Kapler turned to the 21-year-old Santos, who was asked to preserve a 1-1 tie in his second appearance in the Majors.

Santos dazzled in his debut against the Marlins on Thursday, but he quickly fell into trouble in the ninth on Saturday, issuing a leadoff walk to Magneuris Sierra and then misplacing a fastball that Aguilar crushed out to left field to put the Marlins ahead, 3-1. Santos faced three batters without recording an out before giving way to left-hander Wandy Peralta, who allowed an inherited runner to score on an RBI triple by Corey Dickerson. The Marlins added one more run on a sacrifice fly by Jon Berti to extend their lead to 5-1.

Kapler used Rogers and McGee with a four-run lead on Friday, leaving the skipper without his trusted back-end options, but he said he didn’t regret the decision in hindsight.

“I think we have to trust our other bullpen arms to get big outs for us,” Kapler said. “Santos was so lights-out against this team the last time out, so we felt good about him.

“One of the lessons that our less experienced pitchers are going to have to learn is that their stuff plays at this level, but even as good as their stuff is, if you get into a battle with a guy like Aguilar and you fall behind, he’s going to have the advantage. These bumps in the road are to be expected with young pitchers.”

Mike Yastrzemski launched a solo shot -- his fourth homer of the year -- into McCovey Cove to cut the deficit to 5-2 in the bottom of the ninth, but it wasn’t enough to prevent the Giants’ second loss of the year at Oracle Park.

Gausman relied exclusively on his fastball-splitter combination against the Marlins, inducing 21 whiffs in the dominant outing. The 30-year-old right-hander has now pitched at least six innings in each of his first five starts, lowering his ERA to 2.14 on the season, but he received little help from the Giants’ bats, which mustered only five hits.

“Obviously, we want to give him more runs to work with,” outfielder Alex Dickerson said. “He was incredible, as he has been for the majority of his starts here with us over the last couple of years. His splitter was really working well, and when he needed the fastball and needed to reach back, he was able to touch 97 [mph] there a few times. He’s a nightmare to face.”

The Giants were held hitless through the first four innings by Marlins right-hander Pablo López, but they finally got on the board in the fifth, when Dickerson produced a leadoff double to left field and came around to score on an RBI groundout by Austin Slater.

Gausman retired the first 13 batters he faced before giving up a one-out single to Corey Dickerson in the fifth. He carried a shutout into the seventh inning, but then gave up a two-out solo shot to Berti that tied the game, 1-1.

“It’s baseball,” Gausman said. “Sometimes you’re going to pitch terrible and get a win, and sometimes you’re going to pitch great and not have anything to show for it. I think Pablo did a great job over there, too. It was really a pitchers' duel until the seventh inning. You've got to give him credit. His changeup was really nasty tonight. I just think our guys had a hard time. He was really throwing good, quality pitches. It was definitely a pitchers' duel.”

Gausman’s night officially came to an end when Kapler sent out infielder Jason Vosler to pinch-hit for him in the bottom of the eighth. Vosler, who was called up from the alternate training site before Saturday’s game, popped out in foul territory in his Major League debut.