SAN FRANCISCO — When Carson Whisenhunt, Carson Seymour and Carson Ragsdale were all in the same Triple-A rotation, they invented a little game. The three often would walk around the ballpark together, and if a fan yelled out “Carson” the first one to turn around would have to go and sign autographs. 

“Usually it’s Whis,” Seymour explained. “They want his signature.”

Whisenhunt, the organization’s top pitching prospect, will now be hearing those fans at Oracle Park. 

Manager Bob Melvin announced Sunday that Whisenhunt will start Monday against the Pittsburgh Pirates. It’ll be the MLB debut for the 2022 second-round pick, and it’ll come in place of Landen Roupp, who went on the IL on Friday. 

“We’ve been waiting for this for a little bit now,” Melvin said. “We thought maybe he would be here last year, too. He’s our top pitching prospect, I believe. With what’s gone on here with the injury and (Hayden Birdsong) going down (to Triple-A), there’s a need for it. It’ll be exciting to see him pitch.”

Whisenhunt, 23, has a 4.42 ERA in the hitter-friendly Pacific Coast League. His strikeout rate is down, but he has done a better job of staying in the strike zone and has limited homers. He’ll attack the Pirates on Monday with a changeup that is one of the best in the minor leagues and has long been ready for big league hitters. 

The Giants promoted 2022 second-rounder Carson Whisenhunt to High-A after he struck out 20 in 13 2/3 innings with San Jose. He’s got one of the nastiest left-handed changeups you’ll see pic.twitter.com/hu2Rn66UuU

— Alex Pavlovic (@PavlovicNBCS) April 27, 2023

“It’s a legit changeup, for sure,” Seymour said. “The fastball is good. The sequencing is great.”

Seymour was the first of the three Carsons to reach the big leagues, and he hoped to face the New York Mets this weekend since they traded him away a few years ago. Instead, he is likely to back up Whisenhunt on Monday, and he said he’s eager to get that shot. 

Whisenhunt threw seven innings in four consecutive starts earlier this season, but he has not completed six innings in about six weeks. He threw 3 2/3 innings last Sunday, allowing only one run and striking out four. 

The Giants used seven relievers on Sunday, but they currently are carrying 10. To add Whisenhunt, who will wear No. 88, they’ll need to make moves to the active and 40-man rosters, but they should still have plenty of depth behind their young lefty on Monday. They’re currently carrying four pitchers who can qualify as long relief types. 

“It just depends on how efficient he is,” Melvin said of Whisenhunt. “We’d like him to be able to get maybe a little bit deeper into the game than he (did) last time. We do still have some length arms down there to be able to help out, but it just depends on how efficient he is.”

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