A 98th minute Leon equalizer was controversially disallowed to send Morelia through to the Liga MX 2019 Apertura semifinals, after winning the second leg of the quarterfinal 2-1 in Estadio Leon on Saturday.
The stadium erupted when Angel Mena appeared to have sealed Leon's passage, but the referee consulted VAR and found Mena had pushed Efrain Velarde, with the decision debated fiercely on Mexican TV after the game.
Leon had the better of the first half and took the lead through Ismael Sosa in the 52nd minute, leaving the score at 4-3 on aggregate and Morelia needing two goals to go through.
Morelia striker Miguel Sansores responded with a headed goal in the 67th and a deflected shot from Peruvian Edison Flores ended up in the top corner of the goal five minutes later to give the away team the lead.
Leon pushed for a leveler and Mena thought he had it in a game that was end-to-end, with Jose Juan Macias hitting the crossbar in the 102nd.
Leon finished the regular season in second position in the Liga MX table and was considered the strong favorite against seventh-place finishers Morelia.
The game was also stopped for around four minutes late in the second half due to repeated discriminatory chants from Leon fans when Morelia keeper Sebastian Sosa was taking goal-kicks.
Mexico's football federation (FMF) and Liga MX are attempting to crack down on the controversial goalkeeper chant that FIFA has ruled anti-gay, with the FMF fearful of not making Qatar 2022 if it occurs regularly during World Cup qualifying.
Necaxa will be joining Morelia in the semifinals after it defeated Queretaro 3-2 in Estadio Corregidora, also Saturday, to advance 6-2 on aggregate.
Queretaro stormed to a 2-0 lead after 17 minutes -- the goals coming from Marcel Ruiz and Jeison Lucumi -- to give legitimate hope that a famous comeback could be on, although its chances were reduced when captain Luis Romo saw red in first-half injury-time for a high tackle.
Queretaro pushed hard during the opening 20 minutes of the second half, but appeared to run out of steam and it wasn't a surprise when Cristian Calderon, Felipe Gallegos and Maxi Salas netted to send Necaxa through.
In the other quarterfinal second legs on Sunday, America will look to overcome a 2-1 deficit from the first leg against Tigres, while Santos Laguna needs to turn around a 5-2 loss versus Monterrey.