Ghanaian midfielder Gershon Koffie was a second half substitute as Vancouver Whitecaps suffered a 2-0 home defeat to Seattle Sounders at home.
Koffie came off the bench to replace Russell Teibert on 64 minutes but could not help the hosts to bounce back.
The visiting side came out of the gates intent in tempering the feverish crowd. Striker Clint Dempsey once again led the Seattle attack when he played the ball forward and found his scoring partner Chad Barrett escape from the pack to complete a timely finish for the go-ahead goal.
The Rave Green caught the Blue and White defence off-guard when Pappa found a streaking Barrett break into the box. Barrett found the outside corner of the net with a left-foot volley to pad Seattle's lead, 2-0.
Koffie was making his eighth appearance of the season.