NEW YORK (AFP) - Defending champion Rafael Nadal shocked the US Open when he collapsed with cramps during a bizarre news conference while Andy Murray stayed on course for a semi-final clash against the Spaniard. Nadal was talking to journalists two hours after his third round win over David Nalbandian, when he grimaced in pain, screwed up his eyes and slumped in the back of his chair, feeling his right leg. The world number two, a winner of 10 Grand Slam titles, slipped to the floor behind the table where he had been sitting, and out of view of the media, while tournament medical staff was summoned. Scores of reporters and camera crews were ushered out of the interview room deep inside the Arthur Ashe Stadium, but the drama was still relayed into the nearby media centre by the internal television feed.