The Big Ten regular-season champion Gophers (26-6-6) will face the Notre Dame-St. Cloud State winner Sunday for a spot in the Frozen Four.
Condon opened the scoring with a beautiful goal on an end-to-end rush, then clinched the win with a short-handed empty-net goal with 1:48 left.
Cody Wydo and Zac Lynch scored for Robert Morris (19-18-5) late in the second period to cut it to 4-2. David Friedmann also scored, and Dalton Izyk made 43 saves.
The Colonials were making their first NCAA tournament appearance.