Diogo Dalot scored twice as Portugal boosted their hopes of qualifying for the Nations League finals alive with victory over the Czech Republic.
The 2019 winners took full advantage of Spain's loss to Switzerland to move two points clear at the top of Group A2.
Portugal must avoid defeat in their final group match against Spain on Tuesday to reach next summer's finals.
Dalot's Manchester United team-mate Bruno Fernandes scored the second and Diogo Jota added a late fourth.
Needing to avoid defeat in Prague to give themselves a shot at qualification against Spain, Fernando Santos' side responded emphatically to losing their previous Nations League match against Switzerland in June.
Dalot's first-time strike from Rafael Leao's cut-back and Fernandes' finish from Mario Rui's low cross put Portugal in control.
Czech forward Patrik Schick was unable to halve the deficit from the penalty spot before half-time after Cristiano Ronaldo was penalised for handball.
That allowed right-back Dalot to put the game out of reach seven minutes after the restart with a superb left-footed finish from outside the box, before Liverpool's Jota headed in with eight minutes remaining.
Ronaldo, who assisted Jota's goal as he headed a corner into the six-yard box, required treatment in the first half after suffering a blow to the face in a collision with Czech goalkeeper Tomas Vaclik.
The Czech Republic fell to the bottom of the group and must beat Switzerland in their final match to avoid relegation to League B.