BALTIMORE -- Through the first four innings Monday afternoon, Royals starter Carlos Hernández looked like the pitcher he was in the second half of last year. He dominated the Orioles, keeping them off-balance with his four-pitch mix, limiting them to three hits while being as efficient as possible, and needing just 46 pitches to get through four innings.

The fifth is where it came undone.

Baltimore scored six unanswered runs on its way to a 6-1 win, handing Kansas City a series loss at Camden Yards. Hernández still didn’t know quite what hit him when it was all said and done.

“I’m still wondering the same thing,” he said through interpreter Luis Perez. “I lost control in that fifth inning. I don’t know what specifically happened and need to go back and look at video.”

Hernández entered the fifth in the midst of his best start of the season. His command, especially with his fastball, was as good as it’s been all year. The Orioles weren’t seeing his fastball well, and there was a lot of soft contact on his curveball.

But in the fifth inning alone, Hernández threw 35 pitches. Tyler Nevin’s walk and Anthony Bemboom’s double put runners on second and third with one out. Hernández quickly got to two strikes against No. 9 hitter Jorge Mateo with an elevated fastball that Mateo swung through.

Hernández went back to the elevated fastball but Mateo was ready for it this time, lining it into left field for the go-ahead knock. Hernández’s frustration showed on the mound.

“I think once he did give up the single with a man on second and third, I think at that point he was having a little trouble letting that one go,” manager Mike Matheny said. “It doesn’t take long in this game, especially as they roll the lineup over and you’re looking at the top.

“He was just cruising so well, and I think a couple things went against the plan. I think he had trouble reigning it back in.”

Mateo then stole second, and the throw from catcher MJ Melendez landed in center field and allowed another run to score as Mateo went to third base.

“Just rushed it a little bit more than I wanted to,” Melendez said. “Didn’t fully get a grip on it and make an accurate throw. It’s all about learning.”

Hernández regrouped to strike out Cedric Mullins at the top of the order, but the O’s kept coming. Trey Mancini lined an RBI single, and Hernández walked Anthony Santander and hit Austin Hays to load the bases. He then threw a wild pitch that scored a run before Ryan Mountcastle put the finishing touches on the inning with a two-run single.

All six runs were charged to Hernández.

“I felt good. I felt good in the first inning, I felt good in the fourth,” Hernández said. “Still wondering what happened in the fifth. I just have to keep competing. If I keep doing that, then I have the faith that good innings are going to come. … I just have to keep competing and hope that that’s going to take me to the next level.”

The Royals know what kind of stuff the 26-year-old can bring to the rotation -- Hernández showed it last year, with a 3.23 ERA in the second half -- but he’s struggled with consistency this year and has allowed 18 runs in 22 2/3 innings across five starts. His upper-90s fastball isn’t getting whiffs like it did last year (17.5% this season compared to 22.2% in ‘21), and batters are hitting .500 against it even as Hernández throws it almost half of the time (47.7%).

His curveball has been his best pitch, and he’s starting to throw it more, including on Monday.

What made the fifth-inning implosion worse was the lack of offense again. Following Ryan O’Hearn’s first-inning single that scored Bobby Witt Jr. after he stole second, the Royals left nine on base and were 0-for-5 with runners in scoring position. Kansas City is hitting .201 with runners in scoring position this season, which is fourth-worst in the Majors.

“We gave [Hernández] one run,” Matheny said. “When they got one run, they feel like they have to be perfect sometimes. I know that isn’t easy on the pitching staff. Until the offense gets going, there’s going to be more pressure on our pitchers and our defense.

“Not exactly how you want to be going about it, but you got to do your piece. And when things start to unravel, reign it in.”