KANSAS CITY — Despite a runaway seventh inning, Royals right-hander Brad Keller continued his strong second-half surge and continued to show evidence he can be the ace of the team’s rebuild.

Keller threw six no-hit innings Wednesday night before three straight singles forced his exit in the Royals’ 6-0 loss to the Cardinals at Kauffman Stadium.

Using mostly a dominant four-seam fastball that topped out at 96 mph, Keller maneuvered through six innings with five strikeouts and three walks.

The Cardinals hit only two balls hard in that span — a 105.8 mph lineout to right by Paul Goldschmidt and a deep drive to the left-field warning track by Marcell Ozuna, both in the fourth inning.

“He was really good,” Royals manager Ned Yost said of Keller. “The walks hurt him. The walks probably cost him an inning [in terms of pitch count]. He kept coming out of his delivery. He’d get it, then come out of it and lose it for three or four pitches, and that’s when you’d see the 3-0 or 3-1 counts and the quicker walks.

“But he got through six with 96 pitches and no hits. I told [pitching coach] Cal [Eldred] that I’m going to send him back out in the seventh and I’m going to take him to 110 or 115, basically 20 more pitches. I wasn’t going to quick-snatch him out of there. I’m going to give him a chance to get through the inning and win the ballgame.”

Keller seemed to tire a bit in the seventh as his pitch count neared 100. Ozuna jumped on a 3-1 four-seamer and smashed a single to left for the Cardinals’ first hit. Two straight seeing-eye grounders, the last by Matt Carpenter, got the Cardinals on the scoreboard and finished Keller’s night at 107 pitches, 64 for strikes.

“I think he just ran out of gas,” Carpenter said. “He had 96 pitches going into that inning. Ozuna led off with a hard-hit single, Paulie [DeJong] followed up with a quick base hit, and they didn’t have time to make a change.

“You look at his line and maybe it’s not as great as he pitched.”

Keller, though, had mixed feelings about his night. He liked the way he competed but felt his command was considerably off.

“It was a grind, for sure,” Keller said. “I battled my mechanics all night. Felt like I wasn’t ahead of a lot of guys. I felt like my breaking ball hit the grass every time I threw it, so competitive nature took over and I just had to grind through there. I tried to get as many innings as I could.”

Keller’s slider has been an effective pitch in the past two months. But out of 29 sliders he threw Wednesday, only 11 were in the zone.

“Relied on the four-seamer tonight, four-seamer and sinker to just kind of mix it up,” he said. “Didn’t really have much of a breaking ball tonight, so we just had to locate those when we could.”

Though he had a no-hitter through six innings, Keller said that thought barely crossed his mind.

“I was telling the trainers in here,” Keller said, “that most of the time you see guys throw no-hitters it looks like they kind of cruise through innings. I was grinding out there, a lot of pitches, a lot of battled counts. I got 3-2 to quite a bit of guys. It really wasn’t on my mind. I was just trying to get well into the game.”

After Keller left, three more singles, a sacrifice fly and an RBI groundout off reliever Kevin McCarthy made it 5-0, and the Cardinals were on their way to a two-game sweep of the short series.

Meanwhile, the Royals for the second straight night were dominated by a Cardinals starter, this time right-hander Dakota Hudson, who threw six scoreless innings. The Royals were shut out 2-0 on Tuesday night when Jack Flaherty threw seven scoreless innings.

Royals first baseman Ryan O’Hearn, in a season-long slump, was one of the few Royals to see Hudson well. O’Hearn, who hit 12 home runs with a .950 OPS last year in 44 games, is hitting just .175 this season.

But O’Hearn hit two line drives — a single and a double — off Hudson.

“He’s got good stuff, similar to Flaherty yesterday,” O’Hearn said. “Fastball, slider, curveball. I saw him good.

“It’s getting better [for me]. Been putting in a lot of work in. I feel it’s coming. The hits are coming. I’m just trying to get back to being the hitter I know I can be.”