Oswalt lasted 3 1/3 innings, giving up three earned runs and five hits with one walk. He threw 85 pitches, 55 for strikes.
"Breaking pitches weren't there tonight," Oswalt said. "Couldn't get my curveball over, and my slider was kind of flat. The biggest thing is getting the pitch count up. We got up to around 90 pitches, but it was a little quicker than I wanted it to be."
Oswalt got through the first two innings with no damage but ran into trouble in the third. The leadoff man reached after striking out on a wild pitch. A one-out double and back-to-back two-out hits led to a three-run inning.
Oswalt is scheduled to make his next start Sunday with Triple-A Round Rock, where he made his first two starts.
Read more about Oswalt's start here.