Castillo will serve as the Rays' opening pitcher in Sunday's game against the Red Sox, Marc Topkin of the Tampa Bay Times reports.

EDGE Analysis

It will be the first career start for the 24-year-old, who hasn't covered more than 2.2 innings in any of his 29 appearances in the big leagues this season. With that in mind along with the fact that Castillo tossed an inning in relief two days earlier, it's expected that he'll be capped at around one or two frames Sunday before giving way to Jalen Beeks, who will likely serve as the club's primary long reliever.