ARLINGTON, Texas, July 6 (Reuters) - Spain substitute Mikel Merino broke through a stubborn Portugal defence in the 91st minute to earn his side a 1-0 win on Monday and take theme into the quarter-finals, bringing the curtain down on Cristiano Ronaldo's World Cup career.
The midfielder scored six minutes after coming off the bench to take the European champions into the last eight, prevailing where his teammates had been frustrated throughout by a determined and resilient Portuguese 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 World Cup.
Spain will play co-hosts the United States or Belgium, who meet later on Monday, in the next round.
The Spaniards progressed after both teams had shown their attacking intent early, Spain's Mikel Oyarzabal testing goalkeeper Diogo Costa from distance and Portugal's Joao Cancelo lashing his rising shot over the crossbar.
Oyarzabal should have put the Spaniards ahead after eight minutes when a slick move sliced through the Portuguese 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 keeper 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 effort.
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 onto the bar by Pedro Porro's header as Portugal finished the half on top.
Roberto Martinez's side were reduced to playing on the counter after the interval, with Spain dominating possession through Rodri and the increasingly influential Pedri, who saw his attempt steered wide by Renato Veiga's desperate lunge.
Lamine's free kick was tipped over the bar by Costa while Portuguese midfielder Vitinha's strike was deflected into the path of Bruno Fernandes but he shot into the side-netting.
Portugal's defence frustrated their neighbours 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 into his path and Merino slotted the ball into the bottom corner of Costa's goal.
Bernardo Silva almost equalised in the 97th when he rose above Rodri but his header narrowly cleared the bar as Spain advanced to face either the U.S. or Belgium on Friday.
(Reporting by Fernando Kallas; Editing by Ken Ferris)
