OAKLAND -- With recent injuries to Luis Medina and Freddy Tarnok, the A’s are utilizing the openings in their rotation as an opportunity to get a look at a few different starter-type pitchers in longer stints.

Adrían Martínez and Kyle Muller were the two main pitchers who worked in tandem during Oakland’s 4-0 loss to the Royals on Wednesday afternoon at the Coliseum. The duo combined to give the A’s 6 1/3 innings of two-run ball, with each pitcher’s lone earned run coming on a home run.

“We’re working every day to solidify [the open rotation spots], but [we're] also looking at a plan that we may utilize them in roles like we did today,” manager Mark Kotsay said. “We can piggyback a guy or maybe mix and match two starters or two guys that have been working on getting into the rotation. We’re going to continue to work on those types of plans to maximize our success and their success.”

Martínez made 12 starts for the A’s last season as a rookie. In his time with Oakland in 2023, though, the right-hander had pitched solely out of the bullpen with 14 relief appearances prior to getting the start in the series finale. Pitching on three days’ rest, Martínez allowed one run on three hits and one walk with three strikeouts over 2 1/3 innings on 41 pitches.

Muller, who was named Oakland’s Opening Day starter out of Spring Training before struggles through his first 10 starts led to a demotion to Triple-A Las Vegas, put together a second consecutive solid outing out of the bullpen.

Following an appearance of 3 1/3 innings of two-run ball against the Orioles on Friday night, Muller took over to begin the fifth on Wednesday and immediately surrendered a leadoff solo shot to Bobby Witt Jr. However, Muller retired 12 of his next 14 batters and did not allow another hit, finishing with just the one run allowed over four innings.

“I’ve been in a place this year where I’ve had my confidence come from results, and that’s a tough place to be if you don’t get [good] results,” Muller said. “I spent a lot of my time in [Triple-A Las] Vegas kind of figuring out how to get confidence in just my preparation and process. It’s cool that the results are following.”

Recalled on Aug. 16 for what is his third stint with the A’s this season, Muller returned from the Minors having tinkered with the grip on his changeup, a pitch he said can help his fastball -- which maxed out at 94.9 mph against Kansas City -- play up even better.

The revamped changeup is still a work in progress. Muller only threw it three times and all three went for balls. But the hope is that once Muller develops a better feel for the new changeup in games, it will help him inch closer to the ceiling of the No. 1 prospect title he held in Atlanta’s organization at the time he was acquired from the Braves as part of the Sean Murphy deal in December.

“He’s working on his changeup,” Kotsay said. “You saw it a couple of times. I think if we can continue to develop that here, it’s going to make his fastball that much better. We saw a couple of changeups that were down and bounced, but it still comes back with a fastball and gets in on hitters. That’s the growth that we’re looking for. For the most part, he pounded the zone.”

The A’s were denied a chance at what would have been their third series sweep of the season in large part by Royals starter Cole Ragans, who dominated over six scoreless innings on just two hits and 11 strikeouts.

Hot-hitting prospect Zack Gelof’s on-base streak was snapped at 19 games, but even with an 0-for-4 day, Kotsay still found a positive in the rookie’s ability to work an eight-pitch battle in the eighth against hard-throwing reliever Carlos Hernández before smashing a 103.6 mph groundout to second base.

“Zack’s at-bat in the eighth with the bases loaded and two outs was a great at-bat,” Kotsay said. “He positioned it perfectly up the middle. But offensively, we ran into a really good starter today.”