Castillo (4-5) picked up the win over the Athletics on Sunday, allowing two runs on seven hits and no walks while striking out eight over six innings.

Castillo (3-4) earned the win over Atlanta on Tuesday, tossing seven shutout innings while allowing just three hits and a walk. He struck out seven.

Castillo (1-4) earned the win Saturday, shutting out the Rockies over seven innings while allowing two hits and one walk. He struck out nine.

Castillo (0-4) took the loss Sunday against the Cubs, allowing three runs (two earned) on seven hits in six innings. He struck out nine.

Castillo (0-3) took the loss Monday, allowing four runs on nine hits and one walk across 5.0 innings against Toronto. He struck out six.

Castillo (0-2) took the loss Tuesday against Cleveland, allowing four runs on 10 hits and a walk over 5.2 innings. He struck out seven.

Castillo allowed two earned runs on three hits and two walks over 5.1 innings in a Cactus League spilt-squad tie with the Brewers on Friday. He struck out nine.

Manager Scott Servais said Monday that Castillo will start the Mariners' March 28 season opener versus the Red Sox at T-Mobile Park, Ryan Divish of The Seattle Times reports.

Castillo, who fired a couple of 96-mph fastballs during his Cactus League debut Monday against the Reds, is encouraged he has that level of velocity early in camp, Daniel Kramer of MLB.com reports. "It's telling me that I'm healthy," Castillo said. "We're going to continue to be in the same routine, and hopefully that velocity will keep going up."

Castillo (13-7) earned the win Wednesday, allowing two runs on three hits and three walks over six innings in a 3-2 victory over the Angels. He struck out eight.