DC United's poor form continued as New York Red Bulls trumped the Eastern Conference leaders 3-0, while Seattle Sounders tasted derby success.
Bradley Wright-Phillips led the Red Bulls to victory on Sunday, setting up the home side's first goal against DC and then scoring a brace, as the capital club suffered their third straight defeat in MLS.
The result left DC stranded on 44 points at the top of the East's standings, with the Red Bulls (42) and Columbus Crew (41) within touching distance of Ben Olsen's side.
DC started the campaign with just one loss in their opening 10 games to storm to the top in the East, but have lost nine of their subsequent 18 fixtures to drop back to the chasing pack with seven games to play in the regular season.
The Red Bulls had suffered a shock loss at Eastern Conference strugglers Chicago Fire on Wednesday but started strongly against DC, with Wright-Phillips releasing Lloyd Sam into the penalty area in the 33rd minute and the latter fired home from an angle.
It was 2-0 at the break with Wright-Phillips producing a thumping volley from Mike Grella's cross in the 42nd minute, while the former completed his double soon after the hour mark after bursting onto Sacha Kljestan's chip over the visiting defence.
In Seattle, the Sounders had lost six of their past eight league matches but bounced back against rivals Portland Timbers with a 2-1 win.
The home side took control thanks to Obafemi Martins' effort and a penalty from Brad Evans before the interval, but Jack Jewsbury's 58th-minute strike from a corner gave the Timbers some hope.
Portland's best chance to snare a draw came with 12 minutes remaining but Lucas Melano's volley flashed just wide.
The Sounders (38 points) regained sixth spot in the Western Conference with their win, moving ahead of San Jose Earthquakes on games won, while the Timbers (40) sit fifth.
