O'Sullivan (1-0) allowed four runs on 12 hits with three strikeouts over six innings in a win Tuesday against the Athletics.
O'Sullivan did all he had to do as a spot starter: eat up some innings and keep the team in the game. The Red Sox gave him 11 runs of support in the first five innings, so O'Sullivan threw strikes (61 of his 91 pitches) and pitched to contact and let his defense do the work. O'Sullivan will likely be returning to the minor leagues with Eduardo Rodriguez expected to return from the disabled list in time for the next turn in the rotation.