Casey Townsend hit the second-half winner as Chivas USA ended Real Salt Lake's strong start to the season.
After a pair of victories, Real Salt Lake were expected to be too strong for a side who slid to 1-0 defeats in each of their opening two games.
But Townsend prodded the only goal of the game after 72 minutes to earn the visitors their maiden win at Rio Tinto Stadium.
The Chicago Fire beat the Philadelphia Union, who are without a point from three games, thanks to Dominic Oduro's headed goal in the 28th minute.
It was all square in Vancouver where DC United picked up their first point of the season in a goalless draw with the Whitecaps.