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The Spaniards saw off Argentina pair Maximo Gonzalez and Andres Molteni in straight sets 7-6 (7-4) 6-4 in one hour and 49 minutes.

Alcaraz, who began the day with a victory in his singles debut, made a nervy start as he dropped his first serve, but Nadal soon helped to settle the nerves.

They got the vital break in the next game, though there was little to separate the teams after that with a tie-break necessary to put Alcaraz and Nadal in front.

Gonzalez and Molteni rallied in the second set, racing into a 3-0 lead, but could not prevent a fight back as Alcaraz and Nadal won the next three games.

After another vital break for the Spaniards at 4-4, Nadal then served out the match to set up a meeting with either Dutch pair Tallon Griekspoor and Wesley Koolhof or Marton Fucsovics and Fabian Marozsan of Hungary.

It is the match-up that everybody was waiting for at the Olympics, and despite a sluggish start, Alcaraz and Nadal soon turned on the style.

They hit 17 winners, and even though Alcaraz's first service game was not his usual best, they went on to win 46 of their 64 service points (72 per cent).