ST. LOUIS -- The first sign that a promotion for San Francisco pitching prospect Keaton Winn could be imminent came on Saturday. The 25-year-old right-hander had been scheduled to start for Triple-A Sacramento, but the Giants decided to push him back a day.

Winn, who is ranked as the club’s No. 14 prospect by MLB Pipeline, figured he’d pitch after left-hander Alex Wood completed his rehab appearance with Sacramento on Sunday, but Winn still didn’t end up getting in the game.

“After the game, I was a little hot,” Winn said. “I was like, 'Well, I want to throw.'”

The Giants’ plans for Winn soon became clear after he was called into Triple-A manager Dave Brundage’s office for a postgame meeting.

“He did his Brundy little spiel,” Winn said. “He goes, ‘Yeah, I think we’re going to move you to the bullpen. You’re going to be throwing on Monday or Tuesday. They’re in Texas, right?’

"And our pitching coach, [Garvin Alston], was like, ‘No, St. Louis.’ They did get me for a second. They slow-played it really well.”

With the Giants in need of a fresh bullpen arm ahead of Monday’s series opener against the Cardinals at Busch Stadium, Winn earned his first big league callup, taking the spot of fellow rookie Tristan Beck, who was optioned to Sacramento after throwing 4 1/3 innings in two relief appearances against the Cubs over the weekend.

Winn caught a red-eye flight out of Sacramento and landed in St. Louis around 8 a.m. CT on Monday before reporting to Busch Stadium, which is amazingly the first big league stadium he’s visited.

The native of Ollie, Iowa, never got a chance to attend a Major League game as a fan, but Winn grew up rooting for both the Cubs and Cardinals, and he was a big fan of veteran right-hander Adam Wainwright.

“It’s been a whirlwind,” Winn said. “I went out there and sat out there for like 10 or 15 minutes and just tried to soak it in and picture what it’s going to be like.”

Ollie -- a small town of about 200 residents -- is about a four-hour drive from St. Louis, so Winn said he expected to have over 30 friends and family members on hand at Busch Stadium, including relatives from his wife Kailey’s side who happened to buy tickets for Monday’s game weeks ago.

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

Winn had been on a roll in recent weeks, allowing only one earned run with 18 strikeouts over 12 innings in his past three outings.

Listed at 6-foot-4, 238 pounds, Winn mixes a mid-to-upper 90s fastball with a nasty splitter and a slider.

“Keaton’s been good,” manager Gabe Kapler said. “He’s been a good teammate. He’s throwing his split in the zone. His fastball is working well. It’s been more efficient of late.

“It’s a good opportunity for Keaton to show us what he can do.”

Kapler said Winn will likely fill a similar role to Beck, who was used in multi-inning relief stints after making his MLB debut with the Giants in April. The 26-year-old Beck has a 3.73 ERA over 13 relief appearances for San Francisco this season, but he was likely to be down for a few days after his heavy usage against the Cubs.

“It was a tough conversation with Tristan when basically you’re saying, ‘You did everything we asked you to do and did it very well,’” Kapler said. “There’s no real adjustments for Tristan to make. I can see him making meaningful starts for us at times this year.

“If there’s one guy out of this group that you might bet on, it’s Tristan. He’s been that good for us.”