SURPRISE, Ariz. -- With Mason Miller transitioning to a bullpen role for the A’s this season, his electric fastball has led most observers to pencil him in as the team’s closer.

A’s manager Mark Kotsay acknowledged early this spring that while the qualities are there, he would prefer the flamethrowing right-hander to go out and earn the closing role rather than outright anoint him with that title. If Friday’s outing was any indication, it might not be long before Miller solidifies that job.

Miller, ranked Oakland’s No. 2 prospect and top overall pitching prospect by MLB Pipeline, was as dominant as ever in his Cactus League debut. He worked a scoreless eighth inning in the A’s 5-4 loss to the Royals at Surprise Stadium and struck out all three batters he faced.

Miller’s high-octane fastball was in full effect. The 25-year-old kicked off his relief appearance by fanning Rodolfo Durán on a heater that registered 102 mph on the stadium radar gun. The following two punchouts against CJ Alexander and Carter Jensen came on 93 and 89 mph "offspeed" pitches.

“It’s what we saw last year,” Kotsay said of Miller, whose fastball averaged 98.3 mph in the Majors last season. “I don’t know if that [radar] gun was fully accurate, but it was even more velocity today. He mixed in a changeup and had a good slider. A really impressive inning.”

Of his 16 total pitches, Miller’s fastball maxed out at 103 mph and recorded at 101 mph or higher nine times.

“Everything was up,” Kotsay said. “Sometimes, as a starter, you pace yourself. Maybe he’s feeling that ability to let it go a little bit more just knowing he’s going to go out for one inning.”

After he spent nearly four months on the injured list in 2023 due to an ulnar collateral ligament sprain in his right elbow, the A’s are shifting Miller to the bullpen this season in hopes that a lighter workload can help keep him healthy over an entire year. Between five college seasons and three as a professional, the most innings he has ever thrown in one season was 92 2/3 innings in ‘21 at Gardner-Webb University.

The A’s have indicated that Miller could revert to a starting role after this season if he can get through it without injuries. For now, he’s fully embracing his venture into the A’s bullpen, regardless of how long it might be.

“Any role that I’m able to get in the big leagues is exciting to me,” Miller said. “Playing in the big leagues is the goal. Whether that’s starting, in the bullpen, or closing, I’m excited about whatever role that ends up being.”

Wood makes debut

Alex Wood, whom the A’s signed to a one-year, $8.5 million deal this offseason, got the start on Friday for his Cactus League debut. The left-hander worked two innings, allowing three runs on four hits and a walk with two strikeouts.

For a veteran entering his 12th big league season like Wood, Spring Training is less about results and more about building endurance in preparation for a full season. So while he would like a couple of pitches back, mainly the two that resulted in homers allowed to Salvador Perez and Bobby Witt Jr. in the first and third innings, Wood, who previously had pitched in a sim game facing A’s hitters last week, was encouraged by how he felt in his first actual game of spring.

“You never know how the first one is going to go,” Wood said. “Obviously, you want to go scoreless and make a good first impression. But I thought my stuff was alright, just a little erratic command. Overall, I’m glad to get the first one out of the way.”

Wood’s primary focus going forward is to continue growing his chemistry with catcher Shea Langeliers, who was behind the plate for Friday’s outing. He is also improving his slider, which opposing batters hit .288 against last season.

“I’m trying to figure out the shape of [my slider],” Wood said. “It’s easier in bullpens to be able to manipulate shape. A sim game might not be quite as similar as it will be to a real game, so we’ll get all the numbers from today back tomorrow and see where the shape of my slider is at, and really all my pitch profiles and figure out where we go from there.”