The Padres will start Sean O'Sullivan Wednesday against Milwaukee, MLB.com reports. O'Sullivan is taking the rotation spot of the injured Jason Marquis.
O'Sullivan has made a start and two appearances this season for the Padres. Originally expected to serve as long relief, O'Sullivan has allowed five runs over seven innings.
He lost his only start -- July 12 against the Giants -- as he allowed two earned runs over five innings with four strikeouts.