Seattle Sounders failed to cut Vancouver Whitecaps' lead atop the MLS Western Conference following a 2-0 loss at Philadelphia Union.
The high-flying Whitecaps moved four points clear in the west after edging Sporting Kansas City 1-0 on Saturday.
MLS Cup champions Seattle had the chance to climb into second position and within a point of the Whitecaps, who have a game in hand.
However, the Union spoiled the party after Marcus Epps and Roland Alberg inspired the hosts in Philadelphia on Sunday.
Epps broke the deadlock approaching the half-hour mark, before Alberg sealed the victory with two minutes remaining at Talen Energy Stadium.