The Kings scored two third-period goals to break a 3-3 tie. Just over two minutes into the final period, Todd Elik scored off an assist from Francois Breault.
Gretzky added the clincher at 5:35 with his second goal of the game coming on a power play.
The Kings improved to 5-3. Vancouver dropped to 1-4-2.
Each team has two remaining exhibitions before opening the regular season Oct. 4.
The attendance was 9,936, nearly 5,000 short of capacity in the Seattle Coliseum. The NHL will expand by two teams for the 1992-93 season and Seattle is one of eight cities in the running for an expansion team.