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ST. LOUIS -- Before earning his first callup with the Giants, pitching prospect Keaton Winn had never set foot in a Major League stadium. After arriving at Busch Stadium on Monday, the 25-year-old right-hander went out to the field for 10 or 15 minutes and tried to picture what his big league debut would be like.

That vision came to life on Tuesday night, when Winn pitched the final four innings of the Giants’ 10-3 rout of the Cardinals. Winn allowed only one run on one hit while walking three and striking out two, becoming the first Giants pitcher to earn a save in his Major League debut since saves became an official stat in 1969.

“What everyone said was true: You won’t be able to feel your legs,” Winn said. “It was fun. I’ll never forget it.”

Winn said more than 30 friends and family members made the four-hour drive from his hometown of Ollie, Iowa, to be there for his debut, including his parents, Chris and Lynn, who became visibly emotional while watching their son pitch in the big leagues for the first time.

“Super exciting for Keaton and his family,” manager Gabe Kapler said. “Obviously, it was huge for us to cover that portion of the game and save all the other bullpen arms. He’s going to be good. He’s got a chance to be even better than he was tonight. He pitched well. He can pitch better. He was a little bit erratic with his control and command. We’ve seen him be an excellent strike-thrower, so we don’t have any long-term concerns about that. Good, positive debut for Keaton and for our club. But I think there’s an even elevated level of performance from him, as well.”

A fifth-round pick in the 2018 MLB Draft out of Iowa Western Community College, Winn was added to the Giants’ 40-man roster over the offseason and recorded a 4.35 ERA over 12 appearances (nine starts) with Triple-A Sacramento this season.

Ranked the Giants’ No. 14 prospect by MLB Pipeline, Winn topped out at 98.2 mph on his four-seam fastball and leaned heavily on his signature splitter, which he threw 56% of the time and which generated three of his six swinging strikes against the Cardinals. Winn recorded his first career strikeout with his splitter, getting Paul DeJong to swing through a 90.4 mph offering for the second out of the eighth inning.

“He just looks like a polished pitcher already,” veteran Alex Cobb said. “You can tell a lot about a guy’s comfort level when he’s throwing the splitter in hitter’s counts. You can tell it’s one of his favorite pitches to go to, and it should be because it’s falling off the table.”