Andy Murray of Britain reacts to a point against Rafael Nadal of Spain during the conclusion of their rain-delayed semi-final match at the US Open at Flushing Meadows in New York September 7. - Xinhua

Britain's Andy Murray reached the quarterfinals of the Madrid Masters yesterday after struggling past big-serving Croatian Marin Cilic 7-5, 7-6.

However defending champion David Nalbandian of Argentina was easily dethroned 4-6, 2-6 by compatriot Juan Martin del Potro, who is on course for a last-eight meeting with Roger Federer.

Fourth seed Murray started slowly, was broken early and was staring down the barrel in the ninth game of the opening set as Cilic held three set points.

But the Scot roared back with some brave play and helped by some nervous looking shots from the 1.98m Croatian, broke back and then broke again to take the set two games later.

Murray served for the match at 5-3 in the second but Cilic broke back and took it to the tiebreak before the Scot raced away 7-2 to book a place against either US eighth seed Andy Roddick or France's Gael Monfils.

Ninth seed Del Potro, chasing his fifth title of the year, dispatched Nalbandian in just 85 minutes.

Losing the first set 4-6 was something of a recovery by Nalbandian after del Potro had stolen his first two service games for a 3-0 lead, but in the second set he was simply overpowered.

In the first match of the day, French world No. 16 Gilles Simon came back from two match points down to beat Robby Ginepri 6-7, 6-4, 7-6 in an enthralling 2 hour 36 minute duel against the American qualifier ranked 63 in the world.

On Wednesday, Roger Federer advanced to the third round with a 6-3, 7-6 win over Czech Radek Stepanek on his return from a three-week break.

Serbian third seed Novak Djokovic survived a searching test to beat Romanian Victor Hanescu.

Initially Federer had no such concerns, romping to a 3-0 lead as Stepanek's serve fell apart.

But the world No. 30 stepped up in the second set, winning all but one of the points on his first serve, and seized the advantage in the set decider with a sensational drop shot, before pumping his first wildly in celebration.

Two points later he had even greater impetus as he took a 5-3 lead but could not hold on as Federer applied the pressure to take the tie break 8-6 and win 6-3, 7-6 in one hour and 26 minutes.