Castellano allowed four hits and hit a batter while striking out two and walking none over three scoreless innings to earn the save in Sunday's 23-9 win over the Athletics.
Castellano's big-league debut saw him mop up the last three innings of a blowout win to preserve the rest of the Rockies' bullpen. The 25-year-old has had a strong effort in the minors this season, posting a 2.72 ERA, 1.45 WHIP and 53:27 K:BB across 53 innings over 10 starts for Double-A Hartford. He also made a scoreless six-inning relief appearance at Triple-A Albuquerque before his call-up to the majors Saturday. Castellano threw 35 pitches (24 strikes) in Sunday's outing, so he may be able to stick around the big club rather than being immediately optioned out again. He's in the bullpen for now, but if he thrives in a multi-inning role, he could be a candidate for spot starts later in the year.