The loss forced a fifth and final game in the Pacific Coast League semifinals Sunday afternoon.
After the Isotopes scored two first-inning runs to go ahead, 2-1, the Storm Chasers rattled off two big innings in the second and third to build an 8-2 lead.
Omaha added a couple of insurance runs and went into the bottom of the seventh ahead, 10-3.
The first five Isotopes reached base off Doug Davis before Brandon Sisk entered. Sisk didn't fare much better, giving up a pair of singles, a sacrifice fly and Gwynn's three-run shot.
Tommy Hottovy recorded the final two outs -- one a sacrifice fly -- to finally get the Storm Chasers out of the inning.
Only one Storm Chaser reached base the final two innings.
Davis allowed eight runs (seven earned), while Sisk allowed four runs. Adam Moore had a pair of homers.