The Express shut out the San Antonio Mission on Monday night to take a two-game lead in the division with seven left to play.
If Round Rock wins the next three games against the Missions, it will clinch the PCL American Southern Division and a spot in the playoffs for the first time since 2015.
Round Rock right-handed starter Dell Diamond gives Jose Urquidy (5-3, 4.63 ERA) picked up the win and didn't give up a run on three hits with eight strikeouts and a walk over 5.2 innings of work.
Chas McCormick smacked a one-out double to left field to bring home Alex De Goti and give Round Rock a 1-0 lead in the third inning.
The Express took advantage of a throwing error by San Antonio first baseman Travis Shaw in the fourth inning that allowed Taylor Jones and Nick Tanielu to score. Ronnie Dawson and McCormick drove in a run in consecutive at-bats.
Drew Ferguson's line drive bounced off the bag at third base to complete the five-run fourth inning and push the Round Rock lead to 6-0.
The Express and Missions with games each of the next three days with first pitch scheduled for 7:05 p.m. Round Rock lefty Kent Emanuel (4-3, 5.04 ERA) is expected to get the start against San Antonio starter Thomas Jankins (10-4, 4.25 ERA) on Tuesday night.