Payne finished in 2 hours, 1 minute, 58.1 seconds to defend the title she won two years ago in Rome. Martina Grimaldi of Italy took the silver, crossing the finish line 1.8 seconds behind.

Marianna Lymperta of Greece was another 3.7 seconds behind to earn the bronze.

The swimmers competed at Jinshan City Beach, about an hour from Shanghai. The water temperature was 30 Celsius (86 Fahrenheit) degrees about an hour before the race began, just under the newly recommended limit of 31C (88F).

Italian swimmer Giorgia Consiglio, one of the pre-race favorites, was pulled from the water midway through the race because of breathing problems. She was carried to a waiting ambulance and taken to an on-site medical tent.

The Italian team said Consiglio was given oxygen and that she was recovering. She was second at open water worlds last year in Canada.

Safety has become a major concern in open water swimming since the death of American Fran Crippen in the United Arab Emirates last year. Organizers here were using a high-tech sonar system to quickly locate any swimmer that drops below the surface.

Crippen died in October near the end of a 10-kilometer World Cup event in warm temperatures. No one noticed him slip beneath the surface and his body was not found until two hours later.