The Red Sox recalled Rivera from Triple-A Worcester on Saturday.
After turning in a 3.08 ERA and 1.21 WHIP across 38 innings in Triple-A, Rivera will be making his first career start in the majors Saturday, per Ian Browne of MLB.com. It's worth noting that Rivera threw just 29 pitches during his last Triple-A outing and will be working on three days' rest, so he isn't likely to pitch very deep into Saturday's contest. Brett Harris was sent down to Worcester in a corresponding move.