Seattle leapfrogged Dallas in Major League Soccer's Western Conference standings, with Saturday's 1-0 win moving the Sounders into second place.
Mauro Rosales scored the sole goal in the 16th minute as Seattle extended its form surge, having lost only once in the past 13 games.
Dallas suffered its first home loss and conceded its first goal at home in five games, and has only won twice in its past eight matches.
In Columbus, the hosts increased their lead in the Eastern Conference to five points, dropping Philadelphia down to third.
Emilio Renteria scored for the Crew in the 37th minute but the Union equalized five minutes later when Veljko Paunovic connected with an unstoppable header from a Keon Daniel cross.
Andres Mendoza scored the winner from the penalty spot in the 51st as Columbus moved six points above Philadelphia.
In Commerce City, Colorado, substitute Laurent Courtois scored his first goal of the season with an 86th minute equalizer for Chivas at Colorado.
Juan Pablo Angel also scored his first goal for Chivas after being acquired this week from the Los Angeles Galaxy.
Caleb Folan and Jeff Larentowicz scored for the Rapids, who extended their unbeaten streak to six games.
In Houston, Alex Dixon scored his first career goal in stoppage time to give Houston victory over Salt Lake, lifting the Dynamo to second place in the Eastern Conference standings.
In a see-sawing contest, Real's Fabian Espindola opened the scoring in the 28th minute, but Houston dominated the second half and equalized through Brian Ching's goal in the 47th minute.
Luis Gil restored Real's advantage when he headed in a Espindola cross in the 60th, but again the hosts equalized, through Bobby Boswell in the 70th, laying the foundation for Dixon's last-gasp winner.
In Foxborough, Massachussets, Dane Richards scored twice as New York salvaged an away draw at New England.
Milton Caraglio scored twice for the hosts, netting in the 15th and 37th minutes to give the Revolution a 2-0 halftime lead, but Red Bulls' midfielder Richards answered in the 53rd and 87th.
Both teams had a man sent off; New England's Kenny Mansally saw red in the 55th minute, and New York's Teemu Taino followed in the 69th.
