Ruiz rocket fires Philadelphia to Eastern summit
After Dominic Oduro had brought the Fire back on level terms following Michael Farfan's opener for the Union, Guatemalan Ruiz struck from 35 yards out, collecting a clearance from his own free-kick and volleying over Chicago keeper Jon Conway.
The victory moves Philadelphia a point clear of the New York Red Bulls who, without injured French striker Thierry Henry, were held to a 2-2 draw at the Houston Dynamo.
The Red Bulls needed an injury-time header from Moroccan-born Mehdi Ballouchy to get a point from their trip to Texas after goals from Brad Davis and Spaniard Sergio Koke had put Dynamo in front.
The L.A. Galaxy won their local derby against Chivas U.S.A 1-0 to stay on top of the Western Conference - Chad Barrett heading in a David Beckham free-kick in the 26th minute for the Galaxy.
The assist was Beckham's sixth of the season but he is now set to miss the Galaxy's midweek match-up with Houston as he will be playing in former Manchester United team-mate Gary Neville's testimonial game in England.
The Seattle Sounders stay second in the West after defender Jeff Parke scored his first MLS goal in seven years, heading home a Tyson Wahl corner kick in injury time, for a 1-0 win over Sporting Kansas City.
Dallas and Real Salt Lake's game on Sunday was delayed, in the 83rd minute, for one hour 40 minutes due to a rain storm but finished 0-0.