Mitch Keller cruised through a power-packed Padres lineup in his start last Tuesday in San Diego, but as has happened a few times this season, he struggled to maintain that momentum in his next outing.

Keller breezed through the first half of the Reds’ lineup on Monday, recording five outs on 12 pitches. But he could only induce one out in a span of eight Cincinnati batters in the fourth inning, and that allowed the visitors to jump ahead and rout the Pirates, 14-1, at PNC Park.

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The first blemish on Keller’s line was a solo home run on a middle-middle fastball to a Reds player who feasts on those, Eugenio Suárez. The right-hander has shown he can bounce back from that, as he did with a pair of solo shots against him in Detroit on April 22 in a five-inning start that led to a Bucs victory.

“Good or bad, you've just got to think about the next pitch, no matter what,” Keller said. “That's what I was thinking out there.”

And Keller showed that mindset in the third inning Monday, getting a double play after Reds starter Tyler Mahle singled with one out. However, things unraveled in the fourth. Keller allowed two doubles, three singles and two walks, the final of which Mahle drew to chase Keller from the game.

The pitches Keller threw for those results were also fairly even: two fastballs, two curveballs and a slider. The Reds, who outscored the Pirates by 22 runs (30-8) in the first three games they played this season, were squaring up everything in that fourth inning. Three of the five hits Keller gave up in the frame were hard hit (95+ mph exit velocity).

“I felt really good, felt like I was throwing the ball well. It just all started with a jam shot, broken-bat single, just kind of spiraled out of control out of that,” Keller said. “Just got to be better and stop the bleeding early.”

The night ended with seven runs charged to Keller on seven hits and two walks in his 3 1/3 innings. On paper, many things were the same for the right-hander from his start in San Diego. He went fastball-heavy in both outings, with a 69% usage last time and a 68% usage this time. He drew only four whiffs in each start, but the outcomes were completely different due to missed locations, especially toward the middle of the plate.

“In the big leagues, when you don't hit locations, you end up being in the middle of the plate, especially with a club that swings the bat as aggressively as they do,” Pirates manager Derek Shelton said. “You get yourself in trouble, and that's kind of what happened.”

The Pirates have had a tough time against the Reds in their first four games against each another. With the 13-run difference on Monday, the Bucs now have a minus-35 run differential against Cincinnati this season.

“They're a good lineup,” Keller said. “They got on a roll, they all started hitting, so it's pretty apparent in the four games that we've played them already. It's just up to us to stop the bleeding and put an end to it quicker than it's happened.”

While Keller has been able to stop the bleeding in his other starts this season, he hasn’t been able to do it for long periods of time. In three starts when he has completed at least five innings, Keller has recorded a 1.72 ERA with two walks to 17 strikeouts. In his four starts shorter than five innings, as on Monday, he has posted a 15.75 ERA with 14 walks and 19 strikeouts.

The Pirates believe that will even out at some point and Keller will become the “consistent, effective Major League pitcher” general manager Ben Cherington believes he can be, as he told reporters on May 1.

“He’s frustrated by the inconsistency,” Cherington said. “He’s working hard. I really believe in what he’s working on. It‘s important that he continues to pitch.

“I still feel good every time he goes out there. He wants to perform better. Of course, we all want him to perform better. We’ll continue to pour into him to help him do that.”