Mikel Merino made an instant impact off the bench as his dramatic 91st-minute winner earned Spain a 1-0 win over Portugal and a spot in the World Cup quarter-finals. 

Merino finished past Diogo Costa just six minutes after his introduction to seal the win at Dallas Stadium, and a date with the United States or Belgium in the last eight. 

The Arsenal midfielder's late heroics ensured another early exit for Portugal, and ending Cristiano Ronaldo's last shot at World Cup glory, after the five-time Ballon d'Or winner confirmed this would be his final tournament with his country. 

Spain came close to taking an eighth-minute lead when Mikel Oyarzabal beat the offside trap, but after collecting Dani Olmo's inch-perfect pass, he dragged his shot well wide. 

The European champions' bright start continued but they were unable to find a way past Costa, with the Portugal goalkeeper first pushing Lamine Yamal's curling effort to safety before springing quickly back to his feet to tip Alex Baena's shot behind. 

Ronaldo then saw his instinctive volley after good work from Joao Felix kept out by Unai Simon before Nuno Mendes' stinging drive following a short corner routine deflected off the head of Pedro Porro and cannoned against the crossbar. 

Mendes, who had done brilliantly to nullify the threat of Yamal, was forced off with an injury in the 56th minute, and the Spain star was able to get away from his replacement Nelson Semedo which led to Baena testing Costa. 

Yamal then saw a free-kick saved over the crossbar before Bruno Fernandes rifled against the side-netting as a low-key second half appeared set to go to extra time, but having replaced Olmo six minutes earlier, Merino popped up with a late intervention. 

Fellow substitute Ferran Torres turned on Rodri's pass and cleverly slipped in Merino, who took his time before coolly slotting past Costa and into the bottom-left corner to land the decisive blow and dump Portugal out of the competition. 

Ronaldo's World Cup hopes in tatters thanks to Spain's super subs

Ahead of kick-off, Ronaldo said he would not be retiring from professional football but did confirm that this would be his final World Cup with Portugal, but his hopes of landing that elusive piece of international silverware once again slipped through his grasp in North America. 

Ronaldo leaves a legacy behind in the tournament, though. He is the second player to start 25 World Cup games, after Lionel Messi (27), while across his record-breaking six outings at the tournament, he managed 11 goals and two assists, though never finished higher than fourth place. 

Portugal fell short of reaching back-to-back quarter-finals at the World Cup for the first time in their history, and their run here was ended by two inspired substitutions from Luis de la Fuente in Torres and Merino. 

Merino's introduction was somewhat of a surprise given Olmo's impressive outing, but he came up trumps with just Spain's second 90th minute winner at the World Cup, after Peiro against Mexico in 1962.

It was also the third goal for Spain scored and assisted by a substitute on record (since 1996), after doing so against Yugoslavia in 1982 and against Australia in 2014, though La Roja's defence also deserves some credit. 

Ronaldo's 12th-minute effort was the first time Spain had faced a shot on target in the first half at this World Cup, while they became the first team in the tournament's history to keep six successive clean sheets, and they were rarely troubled throughout here. 

Portugal didn’t manage a single shot on target in the second half against Spain, while two of their five shots after the interval overall came in stoppage time as they finished with an expected goals (xG) total of 0.6 from their 10 efforts overall to their opponents' tally of 1.77 from their 15 attempts.