Patton made his major league debut with the Rangers last season, going 1-0 while allowing only one earned run in 9 1/3 innings. In eight appearances at Round Rock this season, Patton has the same 0.96 ERA, allowing one earned run in 9 1/3 innings, with two saves.
Mendez is 0-1 with a 5.40 ERA in 12 relief appearances for the Rangers, allowing seven earned runs in 11 2/3 innings. He allowed runs in three of his last four appearances.
The Rangers made the move before Monday's series opener at Houston.