Teams in MLS do not score three goals in the opening match of a two-leg aggregate goal series. Only three times in since 2002, when MLS last tried three-game playoff series, has a team won the opening leg 3-0. You remember them all, because they’ve all involved the Seattle Sounders.
This year they were on the better side of the 3-0. Back in 2012’s Western Conference Finals they were on the wrong side as they fell behind the LA Galaxy, and would fail to advance. Seattle also dug a hole against Real Salt Lake in the 2011 Western Conference Semifinals.