Mastrobuoni will start at third base and bat seventh in Sunday's game against the Nationals.
Since being reinstated from the 60-day injured list Wednesday, Mastrobuoni has handled a starting role in the infield in five straight games. He's gone 3-for-13 with a walk, a stolen base, two runs and an RBI through his first four starts (three at third base, one at second base), but Mastrobuoni's run of regular playing time will likely come to an end beginning with Tuesday's game against Baltimore. The Mariners plan to reinstate J.P. Crawford (hand) from the 10-day IL that day, and he and Colt Emerson are expected to be prioritized on the left side of the infield over Mastrobuoni, who will move into a utility role.