The Sounders, who sit second in the Western Conference of the MLS, were 3-1 winners against Caledonia AIA of Trinidad and Tobago.
Seattle opened the scoring on the stroke of half-time when Alex Caskey converted Samuel Ochoa's assist.
Ochoa doubled the lead on the hour-mark and although Kareem Joseph pulled back a goal for the hosts their joy ended when Colombian Fredy Montero netted 21 minutes from time.
In Group 3, Honduran side Olimpia and MLS outfit Houston Dynamo drew 1-1 in Tegucigalpa.
Brazilian Douglas Caetano gave Olimpia the lead after seven minutes.
Scotsman Adam Moffat levelled proceedings on 57 minutes and although Houston had Nathan Surgis sent off just moments later they held on for a draw.
The day's other match saw Tauro FC of Panama slump to a 1-0 home defeat against Herediano of Costa Rica.
Whylon Francis scored the only goal of the game in the second half to give Herediano victory in the Group 2 clash.