The Rapids had never lost at PPL Park, and kept that streak going with a come-from-behind draw against the 10-man Union.
The Union went ahead in the 16th minute. A nice passing move sprang Ray Gaddis down the right flank and Conor Casey darted in front of his marker to finish at the near post.
Colorado equalized almost immediately, with Dillon Serna finishing a quick, wide-open counterattack in the 18th minute.
Philadelphia went back into the lead in the 31st minute. Sheanon Williams outjumped the Rapids defense to put a powerful head to Cristian Maidana's corner kick.
The Union added some insurance in the 74th minute. Sloppy defending caused a ball to be deflected in front of the goal and Andrew Wenger swooped in and poached a loose ball to make it 3-1.
Philadelphia's momentum was shortlived. Shortly after Wenger's goal, Union midfidler Michael Lahoud was shown a red card for an attempted clearance inside the penalty area that caught Jared Watts in the face, and Dillon Powers converted from the spot.
Just a few minutes after that, Colorado had erased the Union's lead. Deshorn Brown took a pass from Gabriel Torres outside the box, turned Williams, and picked the low corner to beat Zac MacMath and make it 3-3.
With a record of 4-8-7, Philadelphia is now four points behind New York and the last playoff spot, and the Red Bulls have a game in hand. The 7-5-6 Rapids are third in the Western Conference.