Oswalt gave up four runs on five hits and departed trailing 4-0. It was his shortest stint since a two-inning effort on September 10, 2009.
Oswalt gave up a home run in the first to Jon Jay. He then allowed three successive singles to begin the second inning.
The 33-year-old Oswalt was on the disabled list from April 27-May 16 with lower back inflammation. A three-time NL All-Star, Oswalt has won 10 or more games in nine of his 10 seasons. He threw 37 pitches on Thursday -- 26 for strikes.