PITTSBURGH -- After a strong stretch that helped catapult the Pirates above the .500 mark, the team’s pitching unit faltered on Wednesday night in a 9-6 loss to the Royals at PNC Park.

The nine runs (eight earned) allowed in the series finale were the most yielded by the Bucs since April 7, when the Reds drove in 11 runs to finish their three-game sweep in Cincinnati.

Mitch Keller, who has struggled with command in his early Major League career, was around the zone early against the Royals, but his inability to put away batters early led to a short, pitch-heavy outing.

The first inning was a grind. Keller needed 47 pitches to work through seven batters. He was one pitch away from getting out of the inning, putting Jorge Soler in an 0-2 count. But the Royals slugger fouled off five pitches with two strikes, then lined an RBI double to right-center field on the 11th pitch of the at-bat.

After a seven-pitch walk to Andrew Benintendi in the next at-bat, Hunter Dozier broke the inning open with a two-run triple to quickly put the Pirates in a three-run hole.

“Soler had a really long, good at-bat. He fouled off some good pitches,” Bucs manager Derek Shelton said. “I think it was one of those things that we just didn’t execute the final putaway pitch, and they continued to extend at-bats.”

Keller became only the second Pirates pitcher since 1988 to throw 80 or more pitches in an outing of 2 1/3 innings or fewer. John Van Benschoten threw 84 pitches in his 2 1/3-inning start on July 27, 2007, against the Phillies.

The Pirates’ offense gave the team a fighting chance. Erik González and Jacob Stallings hit back-to-back homers in a three-run fourth, and Todd Frazier’s first hit with the Bucs was a two-run double in the fifth. However, the one steady force in the team’s 4-0-2 stretch of series stumbled on Wednesday.

Pittsburgh’s bullpen, which produced a National League-leading 0.97 ERA from April 13-27, was hit hard by Kansas City. Sean Poppen stepped in to relieve Keller in the third inning, making just his second appearance this season. He yielded a bases-loaded walk before escaping the jam, then gave up two runs on four consecutive singles in the fourth inning.

Chris Stratton, one of the Pirates’ most reliable long relievers, followed Poppen to put up a quick zero in the fifth and allow the Bucs to get within a run. But it unraveled in the sixth for Stratton, who allowed back-to-back run-scoring doubles to push the deficit to 9-5.

“He threw [nine] pitches the inning before and looked really good,” Shelton said. “Yeah, with anything, hindsight is 20/20. … We had full confidence in him. We just didn’t get through it today.”

But the Pirates are going to need to see more even results from Keller, formerly ranked as the club’s No. 1 prospect by MLB Pipeline, this season. Shelton said that Keller has been showing him the work ethic necessary to succeed, and Keller said after his seven-run start vs. the Padres on April 17 that he was confident in himself and his stuff.

“He’s working his butt off between starts, and right now, it’s not translating as much as he would like,” Shelton said. “So yeah, I think there’s some frustration because he’s putting in hard work, and right now, he’s not seeing the fruits of it.”

The Pirates are also not going to back away from the processes they’ve put in place for their young arms like the 25-year-old Keller. Shelton said the coaching staff and organization have clear steps they want Keller to take, and they’re going to trust those steps.

“If not, you may cheat the program in the short run, but in the long run, it’s not beneficial,” Shelton said.

Keller is going to get opportunities to make those gains this season. With his arsenal, including a fastball that touches 97 mph and a sharp curveball evaluators saw as above average during his rise through the Minors, the Bucs know his ceiling is high.

Now, he’s got to continue to make strides to reach it.

“That's half the battle, is just going out there and proving yourself,” Frazier said. “He's a guy that's in his first couple years. He wants to prove himself, how good he is.

“You have to put it in the backburner and move on."