ST. LOUIS — After coming off an injury-shortened start last weekend, Brad Keller was as eager as anyone to step on the mound at Busch Stadium on Saturday to continue his otherwise excellent month of July into August.

But from the first pitch of his start, Keller was instead left searching.

Lacking command on his fastball from the beginning, the Royals’ right-hander walked five in five-plus innings in Kansas City’s 5-2 loss to the Cardinals on Saturday at Busch Stadium. The loss dropped the Royals to 2-6 on the current road trip as they look to avoid the cross-state sweep behind lefty Kris Bubic on Sunday.

“It’s frustrating because I feel like if I had good fastball command tonight, we’d be in that game,” Keller said. “I had a good month, and coming off a start like the last one where I didn’t feel great, I wanted to bounce back from that especially with the way July went. It was frustrating to get out of the delivery that I was doing so well in.”

Keller’s first pitch was a 95 mph sinker to Cardinals right fielder Dylan Carlson almost in the dirt. His second was an elevated four-seam fastball way outside to the switch-hitter.

The third was an elevated sinker and the fourth was another up and away four-seamer.

“First batter, you walk him on four straight,” Keller said. “I don’t think any were close. It was like, ‘Let’s figure it out.’ Dumped two sliders in, and usually the slider helps me get back on my fastball. Got two strikes, then missed a few times on the fastball again.”

Keller walked Paul Goldschmidt before getting a comebacker that could have been a double-play ball. Instead, Keller dropped it and was only able to get the out at first base. Then he struck out Tyler O’Neill on a slider before Hunter Dozier lost Yadier Molina’s fly ball to right field in the sun allowing two runs to score.

“If he walks those two, we miss the opportunity on the double play and still get out of that with a zero, I think there’s a radical shift in that game,” manager Mike Matheny said. “But he never really did find it. He’s going out in the sixth inning with 83 pitches. That’s pretty impressive. That’s just competing with heart and competing with a changeup and slider.

“It’s actually amazing he was able to compete as long as he did without his fastball.”

Those two walks were the first of five in Keller’s five-plus innings. He threw 47 fastballs (four-seamers and sinkers) on Saturday night — and 22 of those were strikes. He only registered one whiff on his four-seamer (11 swings) and none on his sinker (five swings).

What was working for Keller, who allowed five runs on seven hits with five strikeouts, was his slider, which got nine whiffs in the 20 swings it registered, and his changeup.

But without command of his fastball, Keller couldn’t establish the zone and use his full arsenal to his advantage.

“My slider and changeup really kept me in that game,” Keller said. “It was just unfortunate because it kept me in the game so long to give me so many opportunities to find the fastball. I never could.”

Keller struggled to pitch in, which cost him later on as the Cardinals were ready for only one half of the plate. He tried to make mechanical adjustments in-game, but his four-seamer was cutting more than it typically does and he appeared to rush down the mound without keeping much momentum.

“Most guys have those days. They usually end up really, really ugly days,” Matheny said. “But he figured out a way to keep us in the game by pitching without it. That’s his bread and butter. When he’s right, he’s controlling the plate, especially on that third-base side which he wasn’t able to do at all today.”

While he got by on his slider for five innings, he went out for the sixth and allowed two hits off the pitch to end his night and bring in Josh Staumont, who allowed two more hits for one run to score.

At that point, the Cardinals were ready for Keller’s slider.

“You have to move the fastball in and out, got to protect your slider,” Keller said. “They were expecting [the slider] to come. Goldy flied out on a really hard first-pitch slider. They eliminated half of the plate because I couldn’t get my fastball for a strike. Frustrating and difficult.”

Similar to Friday night, the Royals’ offense found momentum in one inning but lacked it the rest of the night. Michael A. Taylor and Hanser Alberto — who played his first game at Busch Stadium in his six-year career — both had RBI singles to put the Royals on the board. But the Cardinals’ bullpen retired 15 of the last 16 Royals batters.