Disaster strikes early
Chicago took an early lead in Chester when David Accam latched on to a poor pass from Ken Tribbett and blasted past the Union defense before slotting in the go-ahead goal in the 3rd minute of play.
Philadelphia attempted to respond minutes later having won a corner when Tranquillo Barnetta took the corner short only to play a one-two pass with Roland Alberg but the Swiss international hit his shot at the edge of the box well wide of the goal.
Frantic play continues
The Union would, however, get their equalizer minutes later when Ilsinho switched the play to Roland Alberg who beat a defender and smashed his shot near post as it rattled around before finding the back of the net in the 11th minute.
Chicago responded in the 13th minute when Accam was found in space with the quick free kick, the Ghana international beat Fabinho all ends up but Andre Blake was there to make the save.
Philadelphia would, however, make Chicago pay in the 15th minute when Barnetta's shot from distance bounced off the post only to bounce again off of Fabian Herbers before be smashed into the back of the net by Roland Alberg for his second of the night.
Play calms down
The later part of the first half would see more relaxed from both sides, but not without its fair share of chances.
Chris Pontius would go looking for the third goal of the night in the 26th minute when he shimmied away from a Chicago defender to get a shot off on the edge of the box, but his shot would drag agonizingly wide of goal.
Ken Tribbett would again be the source of opportunity for Chicago in the 31st minute when he fouled David Accam, but the resulting free kick was hit high and wide of goal by Helsingborg man.
Chicago would again mount an offense on the Union goal late in the first half but Andre Blake and the Union defense were up to the task.
The Union would make them pay in the 45th minute when Alberg once again pounced on a rebound after Fabian Herbers' shot was saved by Sean Johnson but Alberg would put the ball in the net following a block from Gehrig, as the first half ended 3-1 to Philadelphia.
Early second half delight for Philadelphia
The second half would begin much more positively for Philadelphia as Roland Alberg, in the hunt for a hat-trick hit a volley from the edge of the box in the 47th minute, only for Johnson to dive dramatically to make the save.
It would take until the 52nd minute of the match for Chicago to have their first opportunity of the second half when Brandon Vincent found himself on the edge of the Union box, but the defender, out of his natural habitat skied the shot well wide of goal.
The misery would continue for the Chicago Fire away from home in the 55th minute when took down Chris Pontius in the box for a penalty. Roland Alberg would step up for the chance to complete his hat-trick and the Suriname midfielder made no mistake from the spot, converting the penalty to make it 4-1 to Philadelphia.
Chicago gains a foothold
Joshua Yaro would be called into action for the first time in the 63rd minute when substitute John Goossens would cut in from the wing to beat Keegan Rosenberry before having his shot blocked by Ghana international, Yaro.
John Goossens would once again be the danger man for Chicago cutting in from the wing and shooting in the 68th minute, but Andre Blake would prove up to the challenge, saving his shot with ease but stepping out as the Fire earned a corner. Blake would be beaten for the second time on the night as Razvan Cocis would slip past Joshua Yaro on the ensuing corner and tap the ball into the net to pull one back for Chicago in the 70th minute.
Substitute Sebastian Le Toux would have the opportunity to add a fifth goal as he ghosted into the box in the 75th minute, but the Frenchman put Rosenberry's cross well wide of goal as the Union continued to put their foot on the gas in the match.
Chicago would make Philadelphia pay for their miss in the 80th minute when Khaly Thiam converted from short range following a corner from Goossens to make it a one-goal game with just ten minutes to go.
Philadelphia would, however, continue to push toward goal as Keegan Rosenberry forced a save from Sean Johnson when he headed toward goal following a Tranquillo Barnetta corner in the 83rd minute.
Despite their best efforts, Chicago couldn't find an equalizer as Philadelphia held on to extend their unbeaten streak at home this season to ten matches.