The Los Angeles Galaxy have a two-point lead at the top of the Western Conference after being held to a 1-1 draw by the Philadelphia Union on Wednesday.
Landon Donovan gave the visitors the lead in the 24th minute - he has scored his side's last five goals - but Danny Mwanga equalised six minutes from time.
FC Dallas are three points behind the Galaxy after a 1-0 win at home to Toronto FC. Daniel Hernandez scored the only goal of the game from the penalty spot in first-half injury time.
In the day's final game, the Vancouver Whitecaps snatched a last-minute draw with the San Jose Earthquakes. Chris Wondolowski gave San Jose the lead after 39 minutes and they held on until the dying seconds before Davide Chiumiento equalised.