Castillo became the third Boston player in the last two nights to produce the first home run of his career. His blast came in the third inning.
Garin Cecchini went deep on Wednesday and Christian Vazquez hit a towering shot in the second inning of Thursday's game.
Entering the night, Castillo was 4-for-23 with no extra-base hits. The outfielder is signed with the Red Sox through 2020. Later in the game, he added a double.
"Yeah, I actually have been feeling more comfortable," said Castillo. "I feel closer to where I want to be. Like anything else, with some more time and more repetitions I get to feel more confident, but I feel like I'm on my way there."
Castillo also made a nice over-the-shoulder-catch in the triangle area in right-center in the sixth.