Stults gave up a leadoff triple to Emilio Bonifacio, who scored on a groundout, and allowed two more baserunners in the first inning but avoided further damage. The left-hander settled down from there, yielding five hits in 5 2-3 innings with one walk and three strikeouts.
Projected as San Diego's fourth starter, Stults also had two runners on in the third but got out of the jam.
Medica, a first baseman, continued his push for a roster spot with his third home run, which broke a 1-all tie in the fourth.
Seth Smith and Everth Cabrera both had two hits for the Padres.