OMNISPORT

American Jack Sock collapsed on the court at the US Open on Thursday before retiring from his second-round match while leading.

Sock led Belgian Ruben Bemelmans 6-4 6-4 3-6 1-2 when he was finally overcome with cramps and sank to the ground on the Grandstand court.

Trainers rushed to his side, putting a towel over his head and stuffing bags of ice inside his shorts in an attempt to cool him off on a sweltering day at Flushing Meadows.

A wheelchair was brought on court but Sock was helped to his feet and made it off the court upright with assistance.

It was 32 degrees Celsius with 41 per cent humidity and little breeze in Queens on a sunny Thursday.

Weather conditions have been a huge story in the first week of the year's final grand slam event, with Sock one of multiple retirements because of illness or injury.

Sock's fall was surprising, though, as the tournament's 28th seed had dropped only seven games in his first-round rout of Victor Estrella Burgos and had been on court for only one hour, 56 minutes in Thursday's match.