Club America will take a three-goal advantage over Leon into the Liga MX Apertura 2015 quarterfinal second leg on Saturday, after defeating La Fiera 4-1 in the first leg on Wednesday.
Leon took the lead in the Estadio Azteca through Ignacio Gonzalez in the 12th minute, but Club America came storming back to make it 3-1 by half-time.
Paolo Goltz leveled in the 22nd, Mexico international Paul Aguilar put America ahead in the 36th and Dario Benedetto converted from the penalty spot one minute before half-time.
Leon had started the more composed team, even without injured Liga MX top scorer Mauro Boselli -- but America's first two goals came after some poor Leon defending from corners. The third was a penalty call that replays showed was dubious, after Andres Andrade fell to the ground as goalkeeper William Yarbrough slid out.
America gained confidence from the goals and shook off any early nerves after that.
In the second half, Leon had only one shot on goal and America's Ecuadorian international Michael Arroyo put the series virtually beyond Leon -- barring a major shock in the second leg -- with a fiercely struck free-kick from the left flank in the 74th that evaded Yarbrough.
Club America finished the Apertura regular season in sixth position, with Leon in third. The two clubs have won four of the last five Liga MX titles.
Las Aguilas are looking to build on its 12 first division titles, which is one more than rival Chivas as Mexico's most successful.
France international striker Andre-Pierre Gignac scored a memorable first-half goal to help Tigres to a 2-1 victory against Chiapas in its Liga MX Apertura quarterfinal first leg.
Gignac received a lofted pass from Uruguayan Egidio Arevalo and scissor-kicked the ball past goalkeeper Oscar Jimenez from just inside the penalty area in the 21st minute to open the scoring inside Estadio Universitario.
The former Marseille striker -- who was called into the France squad for games earlier this month -- made the shock move to Tigres in June and has so far scored 12 goals in 16 Liga MX appearances.
- Tom Marshall (@mexicoworldcup) November 26, 2015
Tigres dominated possession in the game, but didn't create many clear-cut chances as Apertura surprise-package Chiapas held firm.
Juan Insaurralde managed to sweep in an equalizer in the 66th after confusion in the Tigres defense following a corner, and the home side had already been warned.
Ten minutes earlier, Colombian Aviles Hurtado had headed a golden chance over the bar for Chiapas from close range, after a cross from Silvio Romero left him free at the far post.
Substitute Damian Alvarez then won the match for Tigres six minutes from time when he received a pass from Gignac inside the area and curled a shot into the top corner.
Chiapas finished the regular season in fourth position and came into the game off the back of four consecutive victories, while Copa Libertadores 2015 finalist Tigres finished in fifth.
The away goal rule does count in the Liga MX playoffs, with Chiapas advancing if they win Saturday's second leg in Estadio Zoque 2-1, due to final position in the regular season table.