Petan's hat trick makes him the WHL's first 40-goal scorer of the season and he has a league-best 98 points in 56 games.
Ty Rattie had a goal and three assists for the Winterhawks (45-8-3) while Brendan Leipsic had a goal and two assists.
Colton Sissons scored the lone goal for the Rockets (40-13-4), who dropped back-to-back home games for the first time this season.
Mac Carruth made 31 saves for the win as Jordon Cooke took the loss after giving up five goals on 23 shots through two periods of play. Jackson Whistle replaced Cooke for the third period and stopped all 12 shots he faced in relief.
Portland went 1 for 6 on the power play while Kelowna failed to score on four chances with the man advantage.