Danny Cruz scored twice for the Union (3-3-3), who remained undefeated at home, but probably expected better against the Sounders.
After Rosales got the equalizer for Seattle (1-3-3), the match got chippy. Seattle's Lamar Neagle and Philadelphia's Sheanon Williams were shown red cards in the 85th minute following a scuffle. Five minutes later, Seattle's DeAndre Yedlin was sent off at the beginning of stoppage time, reducing the Sounders to nine men.
All three players will miss their next match.
Eddie Johnson also scored for Seattle after missing the previous two matches with a hamstring injury.