Jesse Forsberg and Roberts Lipsbergs each had a goal and two assists for the Thunderbirds, who lead the first-round series 1-0, and Riley Sheen had a goal and an assist.
Myles Bell and Damon Severson both recorded a goal and two assists for the Rockets and Tyson Baillie had a goal and an assist.
Dylen McKinlay added a single goal to round out Kelowna's offence.
Brandon Glover made 35 saves for the win as Jordon Cooke stopped 45 shots in defeat.
Seattle went 0 for 2 on the power play while Kelowna scored once on six chances with the man advantage.
Game 2 is scheduled for Saturday Mar. 23rd when the Blazers host the Thunderbirds at Prospera Place.