Brendan Leipsic had a pair of goals for the Winterhawks, who took the best-of-seven Western Conference final 4-1, while Taylor Leier scored once and set up two more.
Chase De Leo, Keegan Iverson, Dominic Turgeon and Mathew Dumba also scored for Portland and Oliver Bjorkstrand tacked on three assists.
Jesse Lees, Justin Kirkland and Tyson Baillie supplied the scoring for the Rockets, who won Game 1 before dropping four straight.
Corbin Boes made 35 saves for the Winterhawks as Jordon Cooke turned away 34-of-41 shots in defeat.
Leipsic's night came to an early end when he was assessed a five-minute major and game misconduct for spearing at 16:27 of the third period.
Portland will face the winner of the Medicine Hat Tigers-Edmonton Oil Kings series. Edmonton leads the series 3-1 with Game 5 scheduled for Saturday.