MLS Cup champions LA Galaxy were knocked out of the play-offs after losing 3-2 at Seattle Sounders on Wednesday.
Galaxy's title defence came to an end in the first round of the post-season, with Erik Friberg's 73rd-minute strike condemning the holders to an early exit in Seattle.
The Galaxy's form was alarming heading into the play-offs, having slipped from first in the Western Conference to fifth after winning just one of their last seven regular-season matches.
And the concerns were warranted as Bruce Arena's Galaxy lost out to last season's Supporters' Shield winners in a thrilling encounter.
United States international Clint Dempsey got the ball rolling for the Sounders in the fifth minute, only for Galaxy midfielder Sebastian Lletget to hit back within seconds.
The Sounders restored their lead via Nelson Valdez six minutes later after the Paraguayan latched on to Andreas Ivanschitz's set-piece at the back post.
Gyasi Zardes equalised in the 22nd minute as the see-sawing battle continued, with the USA international's deflected shot from outside the area proving too hot to handle for Sounders goalkeeper Stefan Frei.
Seattle found the back of the net shortly after the restart but Dempsey's goal was ruled out for offside.
The Sounders, however, got their goal with 17 minutes remaining, when Friberg volleyed the ball into the roof of the net.
DC United also won through to the conference semi-finals after coming from behind to beat New England Revolution 2-1.
The Revolution took a 15th-minute at Robert F. Kennedy Memorial Stadium in spectacular fashion thanks to Juan Agudelo, whose bicycle kick left Bill Hamid helpless.
DC, though, did respond before half-time thanks to Chris Pontius after the midfielder glanced a header beyond Bobby Shuttleworth.
And Chris Rolfe, who missed a 75th-minute penalty, made amends eight minutes later when he side-footed in from close range.
The Revolution ended the match with 10 men after Jermaine Jones was sent off for confronting the referee in Washington.
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