The Pirates' No. 5 prospect spun six scoreless frames, struck out seven and surrendered five hits. Keller threw 88 pitches, 58 strikes.
"It's a new level, so [I was] definitely anxious -- nerves, ready to get going," Keller told MiLB.com. "New team, new everything. Same game, though. That's what [manager Brian] Esposito told me from the [Class A West Virginia] Power when he told me the news. He said, 'It's the same game, do the same thing and you'll be fine.' I took that and went with it and it really worked out."
While it's always nice to make a strong impression in a debut, the scoreless start was simply the latest in a string of several from the right-hander.
Keller, MLB Pipeline's No. 80 overall prospect, hasn't given up an earned run in any of his past five starts, a span of 29 innings. During that stretch, he's given up 18 hits and struck out 35.
The rest of the best performances from top prospects Tuesday:
• Austin Meadows (Pirates' No. 2, No. 9 overall) broke out of his slump with a career-high five RBIs. After going hitless in four consecutive games, Meadows stepped up offensively for Triple-A Indianapolis, going 2-for-3 with the five runs driven in. The 21-year-old had a sac fly in the first, a two-run single in the third and a two-run homer in the fifth.
• Ian Happ (Cubs' No. 1, No. 24 overall) hit a go-ahead three-run homer in the ninth inning to win the game for Double-A Tennessee. The 2015 first-round pick went 2-for-3 with a homer and three RBIs and is hitting .253 with five homers and 24 RBIs in 58 games since he was moved up to Tennessee.
• Franklin Barreto (Athletics' No. 1, No. 47 overall) drove in a trio of runs for Double-A Midland. Barreto doubled as part of a 2-for-5 game and now has hits in 16 of his past 17 games.
• Jorge Alfaro (Phillies' No. 4, No. 63 overall) hit his 14th homer of the season and has four RBIs over his past two games after going 3-for-5 with two RBIs for Double-A Reading. The 23-year-old has eight games with three or more hits this season.
• Derek Fisher (Astros' No. 6) continues to rake for Triple-A Fresno. The 23-year-old went 3-for-4 and has hits in 11 of his past 12 games, bumping his average up from .152 to .282 during that span.
• Athletics' No. 7 Yairo Munoz was a triple shy of hitting for the cycle (he has three in 95 games) for Double-A Midland. However, the 21-year-old was still able to go 3-for-5 with two RBIs. Munoz has hit three homers in August, matching the most he's had in any month this season. He also hit three in May.
• Dwight Smith Jr. (Blue Jays' No. 27) hit his 13th homer of the season for Double-A New Hampshire. The 23-year-old went 2-for-2 with two RBIs, including his fourth homer of the month. Blue Jays No. 29 prospect Roemon Fields also went deep for New Hampshire as part of a 2-for-4 night.
• Michael Reed (Brewers' No. 27) had just one hit for Triple-A Colorado Springs, but he certainly made it count. The 23-year-old outfielder jump-started the offense with a grand slam in the first inning and later added a sacrifice fly, finishing 1-for-3 with five RBIs.
• Trevor Clifton (Cubs' No. 8) posted his second consecutive scoreless start for Class A Advanced Myrtle Beach. The 21-year-old threw six innings, gave up three hits and struck out seven. Clifton hasn't allowed an earned run in four of his past five starts and has a 2.72 ERA through 23 outings.
• Andrew Suarez (Giants' No. 8) bounced back from a couple of rough starts with a gem for Double-A Richmond. Suarez scattered six hits across seven scoreless innings, struck out three and walked none while throwing 51 of his 84 pitches for strikes.
• Chance Sisco (Orioles' No. 2) continued his hot streak with his second four-hit game of the season for Double-A Bowie. Sisco was a perfect 4-for-4 at the plate, marking his third consecutive multi-hit game and fifth in his past six contests.
• Chih-Wei Hu (Rays' No. 6) pitched eight scoreless innings for Double-A Montgomery. The 22-year-old gave up just five hits in his second eight-inning start of the season.
• Reds No. 17 prospect Sal Romano cruised through eight scoreless innings for the second time over a three-start stretch for Double-A Pensacola. The 22-year-old threw 58 of his 94 pitches for strikes, struck out six and allowed just two hits.
• Corey Ray (Royals' No. 25) struck out eight (tying his season high) for the second time in as many starts for Class A Advanced Wilmington. The 23-year-old walked one and gave up one run on two hits in 6 2/3 innings. Ray has been tough to hit lately, as the right-hander has given up one earned run or fewer in four consecutive starts.
• Ryan O'Hearn (Royals' No. 28) led the way for the Double-A Arkansas offense in its win over Tulsa. O'Hearn drove in five runs -- three via homer -- as part of his 3-for-5 game.
• Jordan Stephens (White Sox No. 10) is stockpiling strikeouts lately. After fanning 10 in his last outing, Stephens came out and set a season high with 11 for Class A Advanced Winston-Salem. The 23-year-old gave up just three hits and fired five scoreless frames.