Carter Popoff, Brendan Rouse and Brett Kulak scored on the power play for the Giants (16-45-2), who halted a four-game winless streak, and Cain Franson had a goal and an assist.
Rookie Alexander Delnov scored the lone goal for the Thunderbirds (21-33-8), who lost in regulation for the first time in six outings.
Shea Theodore picked up an assist on Delnov's goal, which extended his point streak to five games.
After giving up five goals on 17 shots and being pulled on Friday in a 6-0 loss to the Kamloops Blazers, Vancouver's Lee stopped 23-of-24 shots for his 10th win of the season. Brandon Glover made 30 saves in a losing cause for Seattle.
After going a woeful 2-for-20 on the power-play during its recent four-game road trip, Vancouver scored three times on seven chances while Seattle went 1 for 6.
The Giants dominated the first period, outshooting the Thunderbirds 17-3, and Popoff gave his club a 1-0 lead to take into the first intermission after putting the puck in from the side of the net.
Rouse tipped in a point shot from Kulak at 12:09 of the second period for what turned out to be the eventual winner.
Seattle gradually fought its way back into the game and at 17:32 of the second, while on the 5-on-3, Delnov buried a close-range wrist shot past Lee after taking a pass from Theodore.
Kulak made it 3-1 with a one-timer from just inside the blue line at 12:04 of the third period and Franson added an empty-net goal at 18:11.Suggest a correction