Keller, 20, has a 2.87 ERA and 91:11 K:BB in 81.2 innings at Low-A West Virginia.
Opposing batters are hitting just .208 against Keller, who has not let up since a torrid start to the season. He could see High-A shortly, though the Pirates may proceed cautiously with him as he pitched just 19.2 innings last season due to injury. Still, Keller has firmly placed himself on the prospect map with exceptional control along with the ability to miss bats.