Lukaku has probably looked the best striker at the tournament so far.
It was inaugurated on May 5, 1999 and has a capacity of 57,619 spectators, being the second largest stadium in Andalusia and the fifth largest in Spain.
Portugal look tactically vulnerable and are likely to exit the tournament.
Ronaldo, like Lukaku, was a peripheral figure in the first half but he did go close on one occasion, unleashing a powerful free-kick which had to be parried away by a full-stretch Courtois.
But his positioning and command of his area was second to none, as it has been the entire season at Real Madrid, and in a close contest it was his calming presence which helped push his side into the quarter-final.
It was a let-off for Belgium, who struggled to break down Portugal at the other end, with Romelu Lukaku closely marshalled by Ruben Dias and Pepe, and Eden Hazard sending one first-time shot harmlessly over the bar from the edge of the box.