Castillo recorded eight strikeouts and allowed one hit over seven scoreless innings Saturday in Class A Advanced Salem's 3-1 loss to visiting Lynchburg.
"That isn't easy for a pitcher," he said of his road back, with his agent, Leandro Rodriguez, translating. "I am very happy to be playing games."
Castillo gave up only Nick Ahmed's fourth-inning, broken-bat single and two walks. He fanned five over his final three frames to bring his total to eight, matching a season high. He threw 52 of 84 pitches for strikes and afterward noted his aggressiveness and concentration on the mound.
The 23-year-old right-hander, a free-agent signee out of Venezuela in November 2005, also said the command of his fastball was integral to his bounce-back effort. He left his heater high in the zone against Myrtle Beach on Monday and was charged with five runs on seven hits in five innings.
Otherwise, Castillo has been sharp since his July 5 promotion from Class A Greenville. He's 2-1 -- and easily could be 4-1 -- with a 1.74 ERA through five Carolina League starts.
"I am happy because it's not how you start [but] how you end," he said.
The Hillcats scored three runs on three singles and a walk -- all with two outs -- in the eighth against reliever Jeremiah Bayer (1-2).
Lynchburg starter Gus Schlosser struck out nine over five scoreless innings. He gave up four hits, extended his shutout streak to 28 frames and lowered his ERA to 2.88.