Luna's homer came with one out in the eighth against reliever Jonah Bayliss, giving the Zephyrs their second consecutive come-from-behind victory at Dell Diamond.
Five of the Zephyrs' six wins this season have come against the Express.
The Z's outhit Round Rock 11-5, but let an early 3-0 lead slip away and would not regain it until Luna's blast.
New Orleans scored three times in the first against Wesley Wright, on RBI doubles by Luna and Donnie Murphy and a sacrifice fly by Logan Morrison. The Express responded in the bottom of the inning when Brian Bogusevic hit a two-run homer off Matt DeSalvo.
DeSalvo would hold Round Rock scoreless over the next three innings, before the Express grabbed the lead with two runs in the fifth against Chris Schroder. Lance Berkman, on a rehab assignment from the Houston Astros, tied the game with a sacrifice fly, and the Express took a 4-3 lead on an error by Danny Richar.
Richar made amends by delivering an RBI single in the top of the sixth to score Luna, who had led off with a walk.
Taylor Tankersley (2-1) retired all six batters he faced to pick up the win. Scott Strickland allowed a one-out double in the ninth inning, but struck out Chris Shelton and Yordany Ramirez to end the game and earn his second save.
Game Notes:Former Zephyr Lance Berkman played five innings on a rehab assignment and went 0-for-2 with sacrifice fly and a RBI ... New Orleans is 5-1 against Round Rock this season.
Coming Up:The Zephyrs and Express meet Sunday afternoon at 2 p.m. RH Ryan Tucker (0-0, 1.59) will face RH Josh Banks (0-1, 2.13). RADIO: 106.1 FM WMTI