Trailing Rochelle by 12 points with leading scorer Pete Stefanski sidelined with a sprained ankle, Marmion was in desperate need of a spark.
Senior guard Jeff Garofalo provided it.
Garofalo drained 3 consecutive 3-pointers from the corner to ignite a furious 16-point Cadet run over a four-minute stretch in the fourth quarter.
Alex Theisen buried 4 clutch free throws in the final 24 seconds to secure Marmion's dramatic 55-53 semifinal win Tuesday at the Chuck Dayton Holiday Classic in DeKalb.
The Cadets (8-5) advanced to face Moline (13-1), 56-48 winners over Chicago Vocational, in tonight's 7:30 p.m. championship game.
"When you see that first one go in, you just want to keep shooting," said Garofalo, who tied a season high with 4 3-pointers and finished with 14 points.
"Down the stretch we kept our poise better than we have all season," said Marmion coach Ryan Paradise. "Losing Pete was tough, but our energy never dropped and that's a credit to all the guys who were in there."
The Cadets crashed the boards and clamped down defensively in the fourth quarter, allowing just 2 field goals while forcing 6 turnovers.
A.J. Bohr's 3-pointer after a pair of offensive rebounds gave Marmion a 49-47 lead, its first since 19-18, then Bohr assisted on Ryan Glasgow's basket for a 51-47 advantage with 2:36 remaining.
Rochelle answered with a 3-pointer, but the Cadets flawlessly ran nearly two minutes off the clock before Theisen (9 points, 6 rebounds) cashed in on a pair of free throws.
"Give Marmion credit, their dribble penetration really got to us and we turned the ball over too much when it counted," said Rochelle coach Tim Thompson.
The Hubs executed their inside-outside game plan to perfection in the second quarter, closing with a 14-2 run for a 33-21 lead.
Matt Rosenwinkel tallied 13 of his game-high 15 points in the first half for Rochelle (9-3) while 6-foot-8 center David Newton had 5 of his 10 points.
Marmion limited Rochelle junior guard Grant Prusator, to just 11 points after he had racked up 54 points in the past two tournament games.
"We stuck to our defensive principles better in the second half," Garofalo said. "Once they got the ball inside, we started doubling down on their big guy and started getting turnovers off of that."
Stefanski tallied 10 points for Marmion before leaving early in the third quarter and is not expected to play tonight. Bohr and Glasgow added 7 points each.
Cadets 5-foot-10 guard A.J. Friedman didn't score, but played as huge role in the victory by handling the Hubs full-court pressure throughout and grabbing a game-high 9 rebounds.
"Friedman was a floor general for us in the second half," Paradise said. "I thought he did a great job controlling our pace and getting us into the sets that we wanted."
Marmion connected on just 20-of-57 shots overall and went 9-for-30 in the first half.