The Giants lost Madison Bumgarner on the hill and at the plate before the third inning Saturday night when he was removed with a left elbow contusion after being hit by a line drive in the first.

Austin Slater proved to be his perfect replacement. That's right, an outfielder was exactly what the Giants needed in their 8-4 win over the Cardinals when Bumgarner exited early.

Well, it was more of Slater's bat than anything else.

Bumgarner might be the most feared pitcher with a bat in his hands. Slater replaced him in the lineup in the bottom of the fourth inning and made the most of his opportunity.

Slater sliced the ball just far and high enough over the right-field wall for not only the first pinch-hit homer of his career, but also his first grand slam to give the Giants a 5-1 lead.

"I was looking for that pitch that he threw and he just left it down the middle," Slater said to Amy G after the win. "Going into that at-bat, it was either me or [pitcher] Sam Dyson, and luckily Bochy kept me in there."

The moment the ball went over the wall, Slater let out his emotions as he rounded the bases. And his Giants teammates were throwing a party in the dugout.

"I came in really hot," Slater said. "I think I might have broken a couple fingers coming in. I blacked out for a second. I was super excited."

[RELATED: MadBum exits early in what could be his last home start]

Slater, 26, proved that he can hit for power with 12 home runs and a .529 slugging percentage in Triple-A Sacramento this season. He's been working on lifting the ball all season long, and it's been so far, so good since his promotion to San Francisco. Through four games in the bigs this year, Slater is batting .545 with two homers and nine RBI.

The Giants are trying to figure out where exactly Slater fits in San Francisco. He's now played all over the field in the minors, and being a capable bat off the bench will only help his case for more playing time.