KANSAS CITY -- The Royals seemed on their way to celebrating starter Brad Keller’s 26th birthday the best way a baseball team likes to celebrate: Winning.

But the White Sox and Eloy Jiménez crashed the party.

After Keller dominated a powerful Chicago lineup for seven innings on Tuesday night, he exited with the lead and a chance to become the fourth Royals pitcher to ever celebrate a win on his birthday. But two of the Royals’ higher-leverage bullpen arms came apart in the eighth inning, sending Kansas City to a 5-3 loss at Kauffman Stadium and snapping its six-game winning streak.

“We felt it was time,” manager Mike Matheny said on the decision to end Keller’s night after seven innings and 90 pitches. “He got through seven for us and did a great job. You could tell he was feeling it at times.

“Did his job, gave us a chance to put it in the backend of the ‘pen to finish it off. And he was great today. … He deserved better than that.”

Lefty Jake Brentz came in to face the bottom of the White Sox order and gave up a leadoff double. Then in a two-strike count, Brentz tried to bury a slider but instead hit pinch-hitter Adam Engel. A wild pitch and two groundouts led to a run, so Matheny went to Kyle Zimmer for the final out. The Royals intentionally walked José Abreu -- who entered the game with 75 RBIs -- to face Jiménez, who was 1-for-7 so far in his first series with the White Sox after a nearly four-month long stay on the injured list.

Jiménez fouled off a fastball, and then Zimmer left a slider hanging in the middle of the plate. The pitch was supposed to go down and away, but he lost his grip on it and it slid back to the middle, where Jiménez didn’t miss, sending a mammoth moonshot into the left-center field fountains. Zimmer watched it the whole time, hands on his hips, before striking out Gavin Sheets to end the frame.

“They have a lot of talent and a lot of power in that lineup,” Zimmer said. “You just got to go out and execute. Because if you don’t, you’re going to get hurt. And that’s what happened. It just sucks that one pitch can cost a game, and that’s what happened tonight. And it’s tough.”

After rising to one of the Royals’ high-leverage arms in the first half of the season, Zimmer now has a 8.71 ERA in July, having allowed 10 runs in 10 1/3 innings.

“There’s some mechanical things here and there, but I’m feeling pretty good,” Zimmer said. “And just keep trusting that the results will turn. But it just really sucks feeling like I let down the whole team tonight with that one pitch.”

The loss spoiled Keller’s stellar start. The right-hander allowed a solo homer to Sheets in the fourth but otherwise limited the White Sox to four hits and two walks with four strikeouts. In four starts this July, Keller now has a 2.28 ERA, looking much more like the pitcher he has been the past two years for the Royals. He got off to a suboptimal start in the first half, pitching to a 5.97 ERA over that time, but a mechanical fix in his delivery has him pitching like himself again.

And the results are showing.

In the second inning Tuesday, Keller faced trouble with a bloop single and a walk to lead off the inning. He got out of it with a popup and two swinging strikeouts, one on a filthy slider to Brian Goodwin and the other on a fastball that Leury García swung awkwardly through.

“I think that’s one thing I was missing early on in the season, where my mechanics were so wishy-washy, they’d be there for an inning or I’d lose it in between pitches or something and really struggled commanding the strike zone,” Keller said. “Now I feel like I’m able to go in and out, up and down when we need to. Fastball, slider, changeup, just trying to incorporate the whole repertoire.”

The Royals have won six games in the past week because of quality starting pitching, and they got it again Tuesday. But the offense was held to just three runs and made three outs on the bases, which loomed large as the White Sox mounted their comeback in the eighth.

The slider to Jiménez loomed larger.

“It’s a tough loss. No one wants to see that unfold,” Keller said. “Brentz keeps coming up to apologize to me, and Zimmer does the same thing, and it’s like, ‘Bro, you’ve been nasty all season. One game out of close to 100, it happens.’ I just keep telling them to keep their head up, keep going. We got a game tomorrow, so move on to the next one.”