Youssef En-Nesri’s header late in the first half gave Morocco, who reached the quarter-finals for the first time, a 1-0 lead over Portugal at halftime on Saturday.
En-Nesri, who had earlier hit the crossbar twice, lofted past both Portugal goalkeeper Diogo Costa and defender Ruben Dias to put Morocco ahead in the 42nd minute.
Portugal forward João Félix came close to opening the scoring on two occasions, forcing Moroccan goalkeeper Yassine Bouno to make saves before his strike in the 31st minute narrowly missed the target.
The winner of the match will face either France or England in the semi-finals later on Saturday night.