Ten-man Mali beat nine-man Mexico 2-0 in their first Group D match of the Fifa Under-20 World Cup in New Zealand, as Senegal lost 3-0 to Portugal in their opening Group C fixture.
Mali, who secured the biggest upset of the competition so far through goals from Adama Traore and Dieudonne Gbakle, were forced to defend for much of the first half against Mexico.
Mali seemed likely to be further stretched when Hamidou Maiga was shown a red card in the 56th minute for a clumsy tackle on Hirving Lozano.
But Mexico went from being a man up to a man down in the space of two minutes.
Diego Gama was sent off for an off-the-ball incident in the 66th minute, and Oscar Bernal received a second yellow card for his challenge on Souleymane Diarra in the 68th.
Mali quickly capitalized on their numerical advantage. Adama Traore headed home Youssouf Kone's free-kick 14 minutes from time, and Mali sealed the game three minutes later when Dieudonne Gbakle slammed the ball home.
Mali coach Fanyeri Diarra said the early win lifted pressure from his team.
"I'm amazed by the great shape my players are in physically,'' he said.
"They're up to the task even though they're coming to the end of the regular season at club level."
Mali are top of Group D after Uruguay beat Serbia 1-0.
Senegal began their campaign with a 3-0 defeat to Portugal - previous winners in 1989 and 1991.
Portugal opened the scoring in their Group C encounter through Gelson Martins after only 26 seconds - the fourth-fastest goal in the tournament's history.
Senegal recovered from the early setback with goalkeeper Ibrahima Sy keeping Senegal in the match until the closing stages.
There was little between the two sides until Andre Silva and Nuno Santos both found the back of the net for Portugal in stoppage time.
Also in Group C, Colombia beat Qatar 1-0.
Nigeria begin their campaign against Brazil on Monday in Group E.