Andres Mendoza scored twice to help the Columbus Crew to a 4-1 win as the Colorado Rapids' defence capitulated at Crew Stadium.
Conor Casey headed the Rapids in front in the sixth minute from Jamie Smith's cross but that was as good as it got for the visitors. Eddie Gaven strolled through to equalise after Scott Palguta gave the ball away and Mendoza then took centre stage.
Dreadful defending was again to blame as the Peruvian seized on Kosuke Kimura's misplaced pass to lash home his first goal and, after Casey was dismissed for a dangerous late tackle which caught diving keeper Will Hesmer in the face, Mendoza added a bizarre third for his team.
The Crew cleared a corner and the ball bounced over the head of Kimura on the halfway line, giving the dreadlocked striker a clear run on goal of which he took full advantage.
Tom Heinemann struck the fourth after Gaven's cross was not properly cleared by Tyrone Marshall.
The Chicago Fire came from behind to hold the New York Red Bulls to a 1-1 draw.
Joel Lindpere put New York ahead when Yamith Cuesta's clearance struck him in the chest and the Estonian calmly slotted past keeper Sean Johnson.
A comedy of New York errors led to the Fire's equaliser. Jan Gunnar Solli hacked the ball aimlessly across his own penalty and Carlos Mendes allowed it to bounce off him straight to Marco Pappa, whose low shot from 25 yards bobbled over keeper Bouna Coundoul and into the bottom corner.
The Seattle Sounders also overcame an early deficit as they recorded a third straight win by beating the New England Revolution 2-1.
Sainey Nyassi opened the scoring in the third minute after a well-worked corner but Tyson Wahl equalised with a superb left-footed free-kick.
Alvaro Fernandez grabbed the winner when, after a fine counter-attack, Mauro Rosales and Roger Levesque combined to create the chance and he curled a shot across goal which keeper Matt Reis could not keep out.
Zach Schilawski hit the crossbar as New England pressed for an equaliser but the Sounders held on.