MESA, Ariz. -- Kyle Muller made his biggest statement of the spring in his effort to crack one of Oakland’s remaining spots in a starting rotation that may be finalized in the coming days.

The 6-foot-7 lefty threw 57 pitches through 5 1/3 innings with a fastball biting at 95 mph as the A’s lost 7-1 to the Reds Saturday afternoon at Hohokam Stadium.

Muller -- ranked by MLB Pipeline as the A's No. 5 prospect -- came over from the Braves organization this past December in the three-team deal that also brought Manny Piña, Freddy Tarnok and Esteury Ruiz to Oakland.

Shintaro Fujinami and Drew Rucinski seem to be locks for the rotation when the regular season opens March 30 at home against the Angels, and Paul Blackburn, originally given the Opening Day nod, will start the season on the IL with a finger injury. Ken Waldichuk, Adam Oller, James Kaprielian, and JP Sears are also in the mix.

Against Cincinnati, Muller scattered three runs on five hits and struck out five. The Reds capitalized on a couple mistakes in the fifth, but Muller didn’t need the heat to strike out TJ Friedl on an 83-mph breaking ball in the fourth.

“I was pitch efficient. It’s all starting to come together,” Muller said. “I’m starting to execute better with two strikes. That’s something I didn’t do very well last time. I felt like I was in control pretty much most of the game.”

The start was Muller’s third of the spring, but his first since March 3, when the Royals touched him for four runs (three earned) on five hits in 2 2/3 innings. The 25-year-old hurler is looking for his first consistent opportunity in the Majors after dominating in Triple-A, leading to 11 spot starts with the Braves over the past two seasons.

“He came out that first inning and really pounded the zone with his fastball,” manager Mark Kotsay said postgame. “I think he’s recognizing the importance of the fastball and got through a full five innings. I thought he did a good job.”

Kotsay said the rotation could be decided as early as Tuesday after the team’s upcoming off-day on Monday.

“From the standpoint of the guys collectively that are gonna be used in that rotation, obviously Kyle’s being built up, and he’s done a nice job this Spring Training,” Kotsay said.

Muller’s stuff is nothing new for A’s catcher Shea Langeliers.

Langeliers, who also came up through Atlanta’s system, came to Oakland in the Matt Olson trade with the Braves nine months before Muller’s deal.

The two spent a short time as battery mates in the last series of the 2021 season with Triple-A Gwinnett. Almost a year and a half later, the two find themselves battery mates again with Oakland’s regular season right around the corner.

“I got a text from Ky saying, ‘Call me as soon as possible,’” Langeliers recalled. “I called him and he was like, ‘Dude, we’re teammates again,’ because I hadn’t heard about the trade yet. It was almost like we didn’t miss a beat. Coming up together, I know what he likes to do, I know how he likes to work, I know what pitches he likes to throw. I know how he operates.”

Langeliers caught Muller’s first start this spring back on Feb. 26, when Muller tossed two shutout innings with four strikeouts against the Brewers. Muller’s stuff was even better Saturday.

“He attacked the strike zone, his stuff looked good,” Langeliers said. “That fifth inning, he left one slider over the plate and the guy took advantage. For the most part, I was really, really happy with how it went.”

Muller is preparing for whatever news comes his way next week, whether that means starting 2023 in Oakland or Triple-A Las Vegas.

“I can’t really have any expectations. Whatever they decide to do is what they decide to do,” Muller said. “Obviously, whether it be in Vegas or Oakland, I think I’m gonna be starting every five days.”