Mexico had two players sent off and conceded two goals, all in the space of 14 minutes as it lost 2-0 to Mali in their opening Group D match at the FIFA U-20 World Cup.
El Tri was seemingly in control when Mali's Hamidou Maiga received his marching orders after receiving a second yellow card in the 56th minute.
But Mexico self-destructed when Diego Gama was sent off after an off-the-ball incident and Oscar Bernal earned a second yellow card, both red cards coming within a minute of each other.
Mali took full advantage of its numerical advantage with Adama Traore heading a goal from a free-kick after 77 minutes and Dieudonne Gbakle shooting low just inside the far post after swerving past a couple of despairing challenges on 79 minutes.
Uruguay joined Mali at the top of Group D with a 1-0 win over Serbia.
Despite being second best for the first half, the 2013 finalist took the lead 11 minutes into the final period when Gaston Pereiro finished off nicely from a Facundo Castro pass.
Serbia piled on the pressure in search of an equaliser but the South Americans held on for a first up win.
Portugal impressed early in the tournament with a dominant 3-0 victory over Senegal in their opening Group C encounter.
Gelson Martins fired the fourth-quickest goal in the tournament's history, netting after just 26 seconds, as Portugal pressed Senegal into a mistake, with Martins the eventual beneficiary, finishing into the top corner.
Portugal had to wait another 89 minutes to double its advanatge with Andre Silva scoring with a header and then substitute Nunos Santos adding the third in time added-on with a chip from 35 yards.
In the day's other Group C match, Colombia laboured to a 1-0 win over Qatar.
Joao Rodriguez scored the winner for the South Americans in the 24th minute, but the Asian champion could not put away a number of chances in an improved second half showing.
Qatar will look to make amends against Portugal next up, while Colombia aims to secure progression to the next stage of the tournament when it meets Senegal.