2019 Liga MX Apertura Liguilla semifinals: Everything you need to know

The reigning champion, last season's runner-up and the 2019 Apertura regular-season winner all went out in the quarterfinals of the Liga MX playoffs in a series of matches that were up there with the best the league has seen this decade.

The top four seeds -- Santos Laguna, Leon, Tigres and Queretaro -- are no longer around, meaning the semifinal series have two clear favorites: Club America and Monterrey. However, the way this liguilla has gone so far, the tag of favorite hasn't been something to boast about.

Here's a breakdown of the Liga MX Apertura semis:

Necaxa (5) vs. Monterrey (8)

First leg: Monterrey wins 2-1. Return leg: Saturday, 9:30 p.m. ET.

Necaxa

Six of Necaxa's starting XI were brought into the club last summer, and the club has one of the lowest-valued squads in Liga MX. Necaxa has been flipping players at a profit for a couple of years now and staying competitive, but this is the best team in the club's recent history.

Guillermo Vazquez overcame the loss of captain Ventura Alvarado -- who could be back for the semifinal after a hamstring injury -- in the quarterfinals by employing a back five in the first leg against Queretaro. And it worked perfectly, with the Aguascalientes-based side counterattacking superbly to take a 3-0 lead into the second leg. Crucially, it was Necaxa who looked the fitter in the second half of the return leg, when Los Rayos came from 2-0 down to win 3-2.

Hugo Gonzalez has been outstanding in goal this season and will need another pair of big performances against former club Monterrey (to whom he has been linked once again), Cristian Calderon is in the form of his life at left-back, Jesus Ricardo Angulo has grown from a player with potential to one who affects games, and the aesthetically uninspiring striker Mauro Quiroga continues to prove his worth in front of goal.

Vazquez's team is pragmatic and patient, with only 46.3% average possession this season, which was the least among the eight playoff teams. Against Queretaro, Necaxa was dominated in terms of possession, but not in chances created. The aerial-duels-won percentage (55.9) also highlights a team that can mix it up physically.

Monterrey is a different proposition than Queretaro and won't be sucked into committing too many players forward like Los Gallos Blancos were, but for a Necaxa team that is likely to break up after this tournament -- Calderon and Angulo have both been linked to Chivas -- this represents a huge opportunity for a first title since 1998, when it was still based in Mexico City.

Standard formation: 5-4-1/4-1-4-1. From playing a 4-4-2/4-1-4-1 for much of the tournament, to experimenting with a 5-3-2 and 5-4-1 in the quarterfinals, Vazquez has options up his sleeve. Facing Monterrey, it'd be no surprise if Vazquez opted for a more conservative system.

Most important player: Quiroga. The physical center-forward not only scores goals, but also brings others into the game with his back to goal and is a vital cog in involving Angulo, Juan Delgado and full-backs Calderon and Ricardo Chavez.

Soccer Power Index to win the Apertura: 17%

SPI to advance vs. Monterrey: 43%

Monterrey

Monterrey is back, full of confidence and, according to Tigres coach Ricardo Ferretti, now the favorite for the title. How things have turned around for Rayados since Antonio Mohamed came back to the club: Monterrey hasn't lost in the seven Liga MX games since.

The victory over Santos Laguna in the quarterfinals was a validation of just why Monterrey was one of the favorites going into the tournament, as well as why pundits were so fierce in their criticism when the team was outside the playoff spots for so much of the Apertura. And make no mistake, it wasn't that Santos Laguna played poorly in the 6-3 defeat on aggregate in the quarters, it was just that Monterrey was clinical in picking apart the regular-season first-place team.

Now the talk in Monterrey is about a title, to end a drought that goes back to the 2010 Apertura. Rayados fans would enjoy nothing more than finishing a decade that has seen Tigres become Liga MX's most successful team with a title of their own.

Mohamed has some major selection problems, of the good kind. The first is whom to start up front, with starting striker Rogelio Funes Mori back from injury, but Dutchman Vincent Janssen netted in both quarterfinal games and looks to have regained confidence. Then there is the dilemma of whether Miguel Layun and Rodolfo Pizarro -- also recently recovered from injury -- should come back in for the semis.

One thing that is unlikely to change is Mohamed's compact 4-4-2. The coach's predecessor, Diego Alonso, struggled to harness all the attacking talent within the squad, but Mohamed appears to have found a solution.

December is a big month for Rayados, with the Club World Cup in Qatar also approaching -- meaning that if Monterrey does reach the Liga MX final, it would be postponed until Dec. 26 and Dec. 29 -- and hopes for the team have been completely renewed compared to just a few weeks ago.

Expect Monterrey against Necaxa to be tight, with neither coach wanting to concede space to the other.

Standard formation: 4-4-2.

Most important player: Pizarro.