"I've been working on my approach. I'm thinking middle all the way and looking for my pitch and not trying to miss," Castillo said. "I'm putting my best swing on it and seeing what happens."
With two runs already across on Mariners ace Felix Hernandez, Paul Goldschmidt on first and just one out in the first, Castillo cranked a 1-1 sinker that didn't sink 388 feet to left for his ninth home run.
Two innings later, he again took Hernandez deep, launching a 2-0 changeup 381 feet to left to give the D-backs a 5-0 lead. In doing so, he became just the sixth hitter to hit two home runs off Hernandez in one game and the first since Oakland's Marcus Semien on May 10.
In six games with the Mariners this season, Castillo hit .160 (4-for-25) with just two RBIs. Since arriving in Arizona in a deal that sent Mark Trumbo and relief pitcher Vidal Nuno to Seattle in early June, he has hit .279 with eight home runs, including three against his former team.
"I think it's just giving him at-bats. He's a good hitter," said Arizona manager Chip Hale of Castillo's recent success. "We saw him in Spring Training in Chicago and we knew he was a good hitter and I couldn't figure out why he wasn't getting much playing time."
Castillo stayed inside the fences for the rest of the game, but remained all over the basepaths, reaching on a Kyle Seager error in the sixth and walking an inning later to end Hernandez's afternoon.
His fifth at-bat also resulted in a trip to first base, in familiar fashion. Castillo was drilled by a 95-mph fastball from Fernando Rodney, but the pitch missed his swollen left elbow, instead grazing his left pinky finger.
"It didn't hit me really hard, so it's nothing to worry about," Castillo said. "If they want to hit me, hit me. I don't want to put that in my mind like, 'I'm going to get hit.' I'm not going to change."
With another 2-for-3, 3-RBI effort, Castillo showed the effectiveness of that approach, and Hale said it is one that will continue to improve with more chances.