Derek Blacksher (6-2) earned his sixth straight win allowing four runs on five hits over 7.2 innings of work. He struck out three and walked just one.
Charlie Lisk hit his league-leading 13th home run of the year to put the Grizzlies up 2-0 in the second inning.
Windy City (23-21) tied the score with a pair of runs in the fourth.
The Grizzlies (23-21) answered in the top of the fifth. Stephen Holdren and Michael Campbell each singled to drive in runs and the Grizzlies led 4-2. Robbie Minor added an RBI in the sixth inning to push the lead to 5-2. Holdren drove in his second run of the night with a sacrifice fly in the eighth inning to make it 6-2.
The Thunderbolts got a pair of runs in the bottom of the eighth. Blacksher hit the lead off batter, Doug Coe, then surrendered a two-run homer to catcher Ben Barrone. Blacksher hit a batter and walked another in the inning to put the tying runs on base with two outs.
Joel Boeschen relieved Blacksher to face the dangerous Phil Hawke with the tying runs on base. Boeschen got Hawke to reach for a pitch, striking him out and preserving the lead.
Zach Gray pitched the ninth to earn his fifth save. The first two hitters reached before Gray retired the side.
The win keeps the Grizzlies one game back of West Division-leading Southern Illinois. They are tied with Windy City for second in the division.