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The midfielder scored six minutes after coming off the bench to take the European champion into the last eight, prevailing where his team-mates had been frustrated throughout by a determined and resilient Portugal backline.

A crestfallen Ronaldo left the field to cheers from the sold-out crowd at Dallas Stadium as Portugal exited the tournament a day after the former Real Madrid forward had confirmed the tournament would be his last FIFA World Cup.

"I'm sad to be leaving the [FIFA] World Cup like this," Ronaldo said.

"I gave it my all. I did my best and I'm leaving with a clear conscience. It was my last [FIFA] World Cup, yes, but I'll now have time to reflect and be with my family. I won't be making any rash decisions."

The 41-year-old stopped short of confirming whether he had played his final game for Portugal, saying he did not want a personal decision to overshadow the team's campaign.

"I don't make decisions in the heat of the moment," he said.

Ronaldo, who helped Portugal win the 2016 European championship plus the UEFA Nations League in 2019 and 2025, said he was proud of his contribution to the national team.

"I've won three titles for Portugal; before Cristiano Ronaldo, Portugal hadn't won a single title," he said.

"The biggest title the national team has ever won was in 2016, the European championship, which, to be honest, is just as significant to me as a FIFA World Cup."

Portugal's coach Roberto Martinez also signalled this was his last match in charge of the team.

Spain progressed after both teams had shown their attacking intent early, with Mikel Oyarzabal testing Portugal goalkeeper Diogo Costa from distance and Portugal's Joao Cancelo lashing a rising shot over the crossbar.

Oyarzabal should have put Spain ahead after eight minutes when a slick move sliced through the Portugal midfield with Dani Olmo's incisive first-time pass releasing the Real Sociedad man, who dragged his shot wide of Costa's left post.

Bruno Fernandes then dispossessed Pedri to set up Ronaldo soon after, but Spain goalkeeper Unai Simon blocked the effort with ease.

Costa was then called on to make two saves in quick succession, denying Lamine Yamal from the right and, more spectacularly, Alex Baena's follow-up with a full-stretch, fingertip save.

Simon blocked Joao Felix's header before pushing away Ronaldo's volleyed effort on the rebound, while Nuno Mendes went closest of all with a shot that was redirected on to the crossbar by Pedro Porro's header as Portugal finished the half on top.

Roberto Martinez's side was reduced to playing on the counter-attack after the interval, with Spain dominating possession through Rodri and the increasingly influential Pedri, who saw an attempt steered wide by Renato Veiga's desperate lunge.

Lamine's free-kick was tipped over the bar by Costa while Portugal midfielder Vitinha's strike was deflected into the path of Bruno Fernandes, but he shot into the side-netting.

Portugal's defence frustrated its neighbour throughout the second half but the introduction of Merino for Olmo with five minutes of regulation time remaining proved pivotal.

The quick-thinking midfielder took the free-kick that resulted in Ferran Torres feeding the ball back into his path and Merino slotted the ball into the bottom corner of Costa's goal.

Bernardo Silva almost equalised in the 97th minute when he rose above Rodri but his header narrowly cleared the bar as Spain advanced to face either United States or Belgium in the quarter-finals at the weekend.

Spain coach Luis De la Fuente is not bothered by who comes next.

"It was truly a fantastic game, a final before the final, and, as expected, we suffered until the very end," he said.

"At this stage, we don't care who we face, we're happy to be in the quarter-finals and we're going to give it our all until the end.

"We have many qualities that will make our opponents think we're the team to beat. We have a lot of confidence in ourselves, we're very sure of ourselves, and we'll give our best until the very last moment.

"Our opponents will have to beat us. I think we have many advantages that will make our opponents think the same way."