Moore, 22, has made just one start in the big leagues, pitching five scoreless innings with 11 strikeouts against the Yankees on Sept. 22. That was Moore's first win in the majors. Moore had given up three runs on five hits in 4 1/3 innings of relief prior to that start. He has a fastball in the mid-90s and a plus changeup.
In the minors, Moore was 12-3 with a 1.92 ERA in 27 starts (155 innings) as he split time with Double-A Montgomery and Triple-A Durham in 2011.
The Rangers are 26-21 against left-handed starters this season, including an 18-7 mark at home.
The veteran Shields has been the Rays' top pitcher in 2011, putting up a 16-12 record with a 2.82 ERA in 33 starts (249 1/3 innings). He had 225 strikeouts and 65 walks.
Richard Durrett covers the Rangers for ESPNDallas.com.