An error by Ray Gaddis allowed Javier Morales to equalize in a dramatic finish as the Union went into meltdown mode for the second week running.
The Union opened the scoring early. Conor Casey latched onto a long ball down the right wing, made for the byline, and cut inside. Facing Carlos Salcedo, Casey made a move to get past the defender and played a ball right to Sebastien Le Toux, who had an easy job to tap home.
Real's task was made that much more difficult in the 59th minute, when Lovel Palmer was shown the red card for a clumsy challenge that put Philadelphia's Michael Farfan out of the game.
RSL pulled one back in the 75th minute. Luis Gil made a mockery of Brian Carroll to outleap the Union captain and connect with Javer Morales' free kick to tie it.
The parity didn't last long, as the Union replied immediately. Nat Borchers looked to have handled a long ball out of the Philly midfield, but Antoine Hoppenot was at his best to strip the ball and dish to Casey, who finished to add a goal to his earlier assist.
Le Toux later found himself all alone on a 60-yard breakaway, but hesitated and saw his tame effort pawed away by Josh Saunders.
Philadelphia looked to have done enough to seal a win, but a handball from Raymon Gaddis deep in stoppage time handed RSL a penalty kick, and Javier Morales slammed it in off the post to save RSL's unbeaten run, which now stands at nine matches.