The winner will advance to the championship series against the winner of the other semifinal between Kane County and Clinton.
The Captains took a 6-0 lead, but starter Brett Brach and reliever Owen Dew could not hold it on Monday night.
Brach gave up three runs on five hits and one walk over four innings, striking out five. He left with a 7-3 lead, which Dew nearly torched. The first-year pro didn't get an out in the fifth inning, allowing four hits and three runs as the Loons rallied to within 7-6.
Jimenez and Guilmet came to the rescue.
Jimenez came on with a 7-5 lead and runners on second and third. He struck out the first batter he faced before yielding an RBI single, then got a popout to second base and fly-ball out to center to get out of the jam.
Jimenez worked a perfect sixth and got two quick outs in the seventh before walking a batter.
Manager Ted Kubiak summoned Guilmet and after the runner stole second, the Captains' closer got an inning-ending strikeout. He added two more strikeouts in both the eighth and ninth innings.
Lake County took advantage of some early mistakes by the Loons to lead.
Delvi Cid beat out a ground ball to third base for an infield single to open the game and went to second on a sharp single to right by Tyler Holt. After Casey Frawley struck out, Adam Abraham was hit by a pitch to load the bases. Chase Burnette then hit a potential double-play ball back to the pitcher, but the catcher dropped the throw home, allowing one run to score. Roberto Perez followed with a sacrifice fly to make it 2-0.
In the third, Frawley was hit by a pitch and singles by Abraham and Burnette loaded the bases. Two runs scored on a throwing error, Greg Folgia had an RBI double and Argenis Martinez singled home a run to make it 6-0.
What turned out to be the winning run gave Lake County a 7-3 lead. Jason Smit drew the fourth walk of the inning to force home the run.