JUPITER, Fla. (AP) — The youth movement for the St. Louis Cardinals is in full swing for the No. 5 spot in the starting rotation.

Ever since St. Louis learned that a shoulder injury will likely keep ace Chris Carpenter from pitching this season, attention has turned to the three young right-handers who have a shot to round out the rotation.

Trevor Rosenthal is locked in a competition with fellow 22-year-old Shelby Miller and 24-year-old Joe Kelly, three prospects with limited major league experience. Rosenthal is getting the start Saturday when St. Louis opens its Grapefruit League schedule against Miami.

"It was hard to keep a smile off may face," Rosenthal said. "I’m excited for the games to start, and to have the opportunity to be out there is a lot of fun."

The Cardinals on Friday put Carpenter on the 60-day disabled list due to continued irritation in his spine and right shoulder. General manager John Mozeliak, who has said he doesn’t expect the 37-year-old Carpenter to pitch at all this season, said the move gave the team roster flexibility.

Possessing a fastball that’s been clocked in triple digits, Rosenthal threw 8 2/3 scoreless innings in the playoffs last season after going 0-2 with a 2.78 ERA during the regular season. All of those appearances came in relief.

Even this early in camp, he’s placing great importance on Saturday’s start..

"I think everything matters," said Rosenthal, who’s been a starter in the minor leagues for the past three seasons. "For this first one I’m going to have the mindset that I’m going to go out there and earn it. Every pitch counts right now. ...I think they are going to be watching everything."

Kelly is the most seasoned of the trio. He started 16 games and also made a handful of appearances out of the bullpen last year following a midseason call-up when shoulder issues sidelined Jamie Garcia.

The development of a consistent change-up allowed Kelly to post a 5-7 record with a 3.53 ERA, and the experience boosted Kelly’s confidence heading into this spring.

"If they run me out there they know what they’re going to get," he said. "I know what I can do."

A 2009 first-round draft pick, Miller is also a hard thrower who went 11-10 with a 4.74 ERA at Triple-A Memphis in 2012. During the offseason, he added nearly 25 pounds to a 6-foot-3 frame with hopes that pitching at 220 will add more velocity to a 96 mph fastball while increasing his stamina.

Including the postseason, Miller appeared in seven games last season for St. Louis (one start), earning a win to go with a regular-season ERA of 1.32. He experienced a bit of a scare this week when shoulder soreness forced him to miss a day of throwing. On Friday, Miller was back on the mound for a bullpen side session, afterward saying he felt good.

He was originally slated to start Monday’s game against Houston, but the Cardinals have given that start to John Gast, with Miller’s first appearance in a game probably coming in about a week.

All three pitchers said being a part of last season’s late run gave them an opportunity to bond. That’s made the pressure of this spring’s competition easier to deal with.

"We’re all competitors," Miller said. "You want to win, you want to do your best, and you want to come out on top."

Manager Mike Matheny has yet to give any of the three an edge in the competition.

"They all three showed up ready to take a on a pretty cool opportunity," he said.