British No.1 Andy Murray's defence of the Madrid Masters remains on track in Spain after he cruised past home favourite Tommy Robredo in straight sets.

The Scot, who will play either Juan Martin Del Potro or Stanislas Wawrinka tomorrow on his 22nd birthday in the last eight, took a tight first set 7-5, before demolishing the world No. 17, 6-1 in the second to book his spot in the fourth round.

The first set went on serve until 5-5 but Murray's excellent defence saw him grab the decisive break and clinch the set 7-5.

And the Scot, who overtook Novak Djokovic in the world's top three on Monday, continued where he'd left off in the second set by grabbing a quick break at 1-1.

Home favourite Robredo served his first double fault of the game to give Murray three break points, which he duly converted for a 2-1 lead.

And the British number one didn't look back; breaking his Spanish opponent two more times to take the second set 6-1 in just 33 minutes and clinch a regulation victory.