Ferry Weertman of the Netherlands won an enthralling battle to take the men's 10km open water event off Copacabana beach on Tuesday morning, prevailing by the narrowest of margins to complete a double Dutch triumph following teammate Sharon Van Rouwendaal's victory in the women's race 24 hours earlier.

Weertman only managed to land victory at the last gasp after a dramatic battle to the finish with 10 of his rivals, stretching up to touch the finishing board just fractionally ahead of Greece's Spiros Gianniotis.

The pair were so close that they were given the same finishing time of one hour 52 minutes 59.8 seconds but the 24-year-old European champion Weertman, who won silver at last year's world championships, just did enough to earn the gold ahead of the former double world champion, the 36-year-old Gianniotis.

"It was such a tough race from the start. I did my little share at the front which I don't normally do that early in the race. It made it a little bit tougher for me," said the winner.

"Even after I touched the wall, I wasn't sure I'd won. It took me a while. I called my friends back home and they said 'You won, you won!' and I'm like, 'Oh really?' I couldn't believe it. I still can't believe it," he said.

A couple of seconds behind in a chaotic rush for the finish, there was an equally tight call for the bronze medal with Marc-Antoine Olivier of France just beating Zu Lijun of China to the touch, with both men being timed at 1:53:02.0.

Zu made the best result of male swimmers for China in this event.