ST. PETERSBURG -- The Royals got the starting pitching performance they needed to try to break them out of a slump on Thursday night.

Making his Royals debut, Max Castillo allowed just one run in five innings in Kansas City’s 7-1 loss to the Rays at Tropicana Field -- the only mark against the 23-year-old being the leadoff homer Yandy Díaz crushed in the bottom of the first inning.

But a scoring drought that continued until the eighth inning and a sloppy seventh led the Royals to their fourth straight loss, searching for answers for how to get back on track.

After Castillo, ranked as the Royals’ No. 17 prospect by MLB Pipeline, watched the inside fastball he threw to Díaz travel a Statcast-projected 400 feet into the left-field seats, the right-hander settled down and tore through five efficient innings.

Castillo’s plus changeup was as advertised, showing some nasty movement and appearing especially baffling to the left-handed hitters populating the Rays’ lineup.

"He had good stuff, man,” switch-hitter Roman Quinn said. “He had a really good changeup -- really good changeup.”

But Castillo’s slider was a priority for him when coming over to the Royals, and showed good depth, playing off his fastball.

“He was at 93-94 mph, but you could tell it was getting on guys, speeding them up to make the slider more effective,” manager Mike Matheny said. “For as young as he is, really impressed with how he held himself on the mound, how he executed, how he was able to locate.

“Everything we could ask, he did.”

Castillo was on a limit of about 70-75 pitches because he was still building up as a starter at Triple-A Omaha after the Royals acquired him from the Blue Jays in a Trade Deadline deal. But he cruised through five innings at 68 pitches, allowing three hits to go with one walk and three strikeouts.

With the way Castillo threw on Thursday, it’s easy to imagine him as a starter or reliever for the Royals moving forward.

“It’s been a while since passing that limit,” Castillo said. “Going through it today felt good. “I felt good. Had a lot of trust in myself to execute pitches.”

Lefty reliever Amir Garrett continued his run of success with 1 1/3 scoreless innings. He has not allowed a run since before the All-Star break, covering 12 1/3 innings with nine strikeouts.

But things deteriorated quickly when Matheny called on Brad Keller with one out in the seventh for his first relief appearance since 2018. The Rays’ one-run lead quickly grew to five when Keller -- who was moved from the rotation to the bullpen this week with the club’s hopes of pitching him in high-leverage spots this season -- allowed six consecutive hits and a wild pitch before getting the final two outs of the inning.

The first three hits that Keller yielded were all ground balls, but they were all struck 102 mph or harder.

“With an out, the bottom of the order, down a run, we really liked giving Brad the opportunity to come in,” Matheny said. “… The actual life on the ball, the sink, the velocity, those are things that definitely played up. Good bite on the slider, maybe too much at times. It’s a shame it turned out the way it did.”

The inning loomed large shortly after because the Royals’ offense showed a spurt of life with Michael Massey’s first Major League homer in the top of the eighth, one that would have tied the game had the Rays been kept at bay in the seventh.

Massey has hit safely in nine of his past 10 games and he has displayed the power he’s shown in the Minors, but he’d been searching for his first homer until he crushed a fastball off Shawn Armstrong and watched it stay just fair inside the right-field pole.

“I knew I got it good, and I was like, ‘The only thing this can’t do is hook,’” Massey said. “And then it started to. Luckily, there’s no wind in here, so it straightened out.”

Massey’s home run snapped a 33-inning scoreless streak for the Royals’ offense. They entered the opener of this four-game set not having scored since the first inning on Monday against the Twins, and the Rays shut them down for seven innings.

“Those things happen over the course of 162 games,” Massey said. “You’re going to have ups and downs, times where you’re not as clutch as you are, and you’re going to have times where runs come easy. … Tonight, we got on the board a little bit, and hopefully it’ll carry into tomorrow.”