Club America won 3-1 at Pumas in the second leg of their Liga MX semifinal clash but couldn't recover from a 3-0 defeat at the Estadio Azteca, going out 4-3 on aggregate.
After a bright start, Darwin Quintero grabbed a lifeline for the visitors when he scored twice in under 30 minutes.
Pumas continued to ride their luck as Las Aguilas pressed relentlessly for a third.
But frustration started to pay its toll on Las Aguilas, and Paolo Goltz and Rubens Sambueza were sent off in the second half.
Pumas immediately made their advantage count, and Javier Cortes stabbed home the 4-2 for the Universitarios.
Andres "Rifle" Andrade set up an exciting finale when he slotted past Alejandro "Pikolin" Palacios with three minutes to go in the game. But Guillermo Vazquez's side held on to a controversial win at Ciudad Univeritaria to get one over the crosstown rivals.
Pumas will now face Tigres in the Liga MX Final following Tigres' 2-0 win over Toluca at the Estadio Nemesio Diez.
Ricardo Ferretti's side had a host of chances in the first half, but it took 69 minutes for Tigres to grab the breakthrough when Damian Alvarez played Javier Aquino through.
Damian Alvarez then scored with seven minutes to go after Andre-Pierre Gignac set up the winger with an easy header to seal the tie in favor of Tigres.
With both finalists determined, the first leg of the Liga MX final is expected to be played on Thursday, and the return leg is to be played on Sunday at Pumas' Ciudad Universitaria.
You can watch highlights of both games below: