PITTSBURGH -- Mitch Keller arrived in Pittsburgh in 2019 as the Pirates’ top prospect. The journey at the Major League level has been bumpy for the right-hander, but it reached a low point when Keller was optioned to Triple-A Indianapolis on June 12 with his ERA at 7.04.

The Pirates have shown optimism in what Keller accomplished while at Indianapolis, where he recorded a 3.21 ERA with 39 strikeouts in 28 innings over eight outings (six starts). But whether those gains will translate to results in the Majors has yet to be determined.

Keller’s first start back with the Pirates in Sunday’s 15-4 loss to the Phillies at PNC Park was in some ways encouraging and in other ways a recurrence of past issues. The 25-year-old was able to work five innings on 80 pitches without issuing a walk, but he was tagged for four runs on eight hits, including five doubles.

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The extra-base hits were a symptom of the hard contact that Keller routinely allowed throughout his start. Eleven balls put in play had an exit velocity of greater than 95 mph, which Statcast classifies as “hard-hit,” and six of them went for hits. It’s not a new trend: Keller is in the bottom 3% in the Majors in hard-hit rate.

Why the hard contact? A lot of it came down to Keller's inability to locate his offspeed pitches consistently. Of the eight hits he afforded to Philadelphia, six came off his curveball, slider and changeup -- and all were either up in the strike zone or middle-cut.

“Obviously, the results weren’t there,” Keller said. “... [But] I think I executed a lot of good fastballs. I felt really good, confident. I just think in the first and second innings, my breaking ball stuff was up in the zone.”

One of the reassuring signs was the zero in Keller’s walks column, which is a turn from how he finished his stint in with the Indians. In each of his final three starts at Triple-A, he issued three walks, leading to mixed results in the numbers of runs he allowed.

However, Keller went five innings without doling out a free pass against the Phils -- only the second time this season he’s been able to do that. Attacking the zone has been a major point of emphasis both at Indianapolis and during Keller’s pregame work.

“He commanded the ball on the plate,” manager Derek Shelton said. “He left some balls over the middle that got hit, but he was on the plate, so that's definitely a positive sign."

The Pirates have faith in Keller, and Keller has faith that he can be a good Major League pitcher. General manager Ben Cherington has been reassured by some of the reports he’s received out of Triple-A while the Bucs’ former No. 1 prospect worked to simplify his game -- as Keller put it, “feeling athletic, getting some good tempo and some good rhythm.” Sunday was the start of the righty getting more chances to show that progress.

"I think it's also a good reminder or example of … development is not isolated to the Minor Leagues,” Cherington said on 93.7 The Fan before Sunday’s game. “Guys can get better everywhere, including the Major Leagues."

But the Pirates are also going to have to balance developing their younger arms -- a group of six or seven rotation options -- at the Major League level while mixing in a group of veterans like Chad Kuhl and Steven Brault.

One or two mixed outings won’t affect long-term plans for pitchers, but in the short term, the jam may make it harder for some to get MLB reps on schedule. Keller will get more looks, but how many more this season has yet to be determined.

“We've talked about people getting opportunities,” Shelton said. “Some guys are already there. Some guys we can potentially call up and give starts like we've done with some of these other guys. And I think throughout the entire year with these opportunities, we're constantly evaluating, so it's not just the last two months, but the full scope of the year."