The Red Sox optioned Rivera to Triple-A Worcester on Thursday, Chris Cotillo of MassLive.com reports.
Rivera made his major-league debut out of the bullpen Wednesday versus the Yankees and was impressive, fanning three over 3.1 shutout innings while yielding just one hit. Despite the good first impression, the plan was always to send Rivera back to the minors so that he can stay stretched out as a starting pitcher. The lefty could get another look later this season when a need arises.