The Seattle Sounders made a poor start to their MLS campaign with a 1-0 defeat against the Montreal Impact on Saturday.
Seattle, who lost last season's Western Conference final to the Los Angeles Galaxy, began their season with a winnable home clash against Montreal, who only entered the competition last year.
But despite 39,000 fans packing into the CenturyLink Field for the match, the Sounders slumped to an opening-day defeat.
The game's only goal came after 35 minutes when Davy Arnaud produced a terrific finish.
Felipe set up the goal with a scooped pass over the top of the Seattle defence and Arnaud needed just one touch to lift the ball over Seattle goalkeeper Michael Gspurning and into the back of the net.
The Sounders hit the post twice in a bid to score an equaliser, with Brad Evans and Eddie Johnson both denied by the woodwork.
Sporting Kansas City came from behind to record a 3-1 win over the Philadelphia Union at PPL Park.
Philadelphia - who lost the last three games of the 2012 season - claimed the lead after 18 minutes when Sebastien Le Toux converted Keon Daniel's assist.
The winners equalised four minutes before the break when Graham Zusi converted the rebound from Benny Feilhaber's saved shot.
Zusi turned provider for his side's second goal on 66 minutes, with his excellent free-kick headed home by Oriol Rosell.
The match was sealed with six minutes to play when Zusi played in Chance Myers, who cut back for Claudio Bieler.
And the Argentine finished with aplomb to help Sporting Kansas City to the perfect start in the 2013 season.
Other results saw the Vancouver Whitecaps and FC Dallas win 1-0 at home against Toronto FC and the Colorado Rapids respectively.
Columbus Crew won 1-0 at Chivas USA thanks to a goal from Argentine Federico Higuain while Houston Dynamo scored twice in the last 10 minutes to beat DC United 2-0.