The win gave Rockford a 2-0 series lead in their Western Conference Central Division Final.
For the second straight game the Moose scored the game's first goal but Rockford came back to take control and post a win.
Chris DiDomenico, Carl Dahlstrom and Andreas Martinsen added singles for Rockford.
Collin Delia turned aside 33 shots for the IceHogs.
Brendan Lemieux scored the lone goal for the Moose.
Eric Comrie stopped 17 shots for Manitoba.
Brendan Lemieux scored with just under four minutes remaining in the opening period as he deflected a Nic Petan feed past IceHogs goaltender Collin Delta to put Manitoba up 1-0 at 16:03.
The goal was his 3rd of the playoffs.
Rockford evened the contest at 18:38 when Tyler Sikura scooped up a redbound off a shot from defenceman Victor Svedberg to make it 1-1 and fired the disc past Moose goaltender Eric Comrie.
The goal was his 3rd of the post-season.
Chris DiDomenico gave the IceHogs the lead 4:45 into the second period when he cut off a puck along the right side boards before working his way to the high slot before wiring a low wrister past Comrie to make it 2-1.
Carl Dahlstrom blasted a puck past Comrie just over the 16 minute mark to give Rockford a 3-1 lead at 16:03.
Gustave Forsling hit Dahlstrom with a crisp partner pass along the blue line which he stopped before leaning into a slapshot that sailed past Comrie.
The goal was his 4th of the playoffs.
Andreas Martinsen added an empty netter late in the third period to seal the in for the IceHogs.
The series resumes Wednesday in Rockford.
SHOTS-ROCKFORD 22 MANITOBA 34