Merino's winner in the first minute of added time finally separated the two Iberian rivals after a tightly contested encounter, sending the European champions into a quarter-final meeting with either the United States or Belgium.

Luis de la Fuente's side enjoyed the better of the early chances, with Mikel Oyarzabal dragging a clear opportunity wide before Diogo Costa produced excellent saves to deny Lamine Yamal and Alex Baena.

Portugal gradually settled into the contest and came closest before the interval when Nuno Mendes' powerful effort deflected onto the crossbar via Pedro Porro, while Cristiano Ronaldo forced Unai Simon into a save from a tight angle.

Spain continued to dominate possession after the restart, but clear-cut openings remained scarce as Portugal defended resolutely and looked to threaten on the counter-attack.

With extra time appearing inevitable, Spain found the breakthrough in stoppage time. Ferran Torres picked out Merino inside the penalty area, and the midfielder kept his composure to steer a low finish beyond Costa and send La Roja into the last eight.

The victory extends Spain's unbeaten run at the tournament and maintains their remarkable defensive record, with De la Fuente's side yet to concede a goal at the 2026 FIFA World Cup.

Spain will now turn their attention to a quarter-final showdown as they continue their pursuit of a second World Cup title.

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