The best-of-seven series is now tied at a game apiece. Game 3 goes Tuesday in Portland.
Nicolas Petan broke a 2-2 deadlock late in the second period for the Winterhawks while Paul Bittner and Dominic Turgeon built Portland a two-goal lead.
Rourke Chartier and Dillon Dube responded for the Rockets.
Kelowna's Jackson Whistle turned aside 29-of-32 shots in defeat.
Portland went 1 for 4 on the power play while the Rockets scored twice on four chances with the man advantage.
WHEAT KINGS 3 HITMEN 2 (OT)
BRANDON — Tyler Coulter scored 51 seconds into overtime as the Wheat Kings slipped past Calgary to take a 2-0 lead in the Eastern Conference final.
Jayce Hawryluk and Peter Quenneville also scored for Brandon, which got a 22-save outing from Jordan Papirny.
Michael Zipp and Adam Tambellini found the back of the net for the Hitmen. Brenden Burke kicked out 43-of-46 shots in defeat.
Calgary hosts Game 3 Tuesday.