Shaw got his first rehab start in San Antonio, going 0-3 as the Missions collected just two hits in the 4-0 loss to the Express.
Mauricio Dubon and Cory Spangenberg each got a hit but no other Missions reached base against Cy Sneed and Gabriel Valdez. Sneed was a former Brewers farmhand, but was traded a few years ago in the deal to acquire Jonathan Villar.
Bubba Derby continues to look for his first win of the season, going 3 2/3 innings allowing all four runs for Round Rock.