 Mills left Forest shortly before the end of 1981–82 to join the Seattle Sounders of the North American Soccer League in March 1982.He made 31 appearances, scored 5 goals and recorded 7 assists in the 1982 North American Soccer League season as Seattle finished first in the Western Division.He started for Seattle in Soccer Bowl '82 before being substituted for Roger Davies, and the match was won 1–0 by the New York Cosmos with a 31st-minute goal scored by Giorgio Chinaglia.