In the men's race Marcel Schouten from The Netherlands gained his first World Series win by just one second, coming home in front of four Brazilians in 1 hour, 56min, 10.2sec, while in the women's event the top three were separated by just four tenths of a second.

Ana Marcela Cunha from Brazil won that race in 2:05:42.90, to gain her 20th World Series title.

In the men's race 11 of the 18 starters were still packed together on the backstretch of the final lap.

Schouten managed to open up a four-body length lead, however, which proved enough to gain him his first World Series win.

The Brazilian Fernando Ponte finished second, just three tenths of a second ahead of his compatriot Diogo Villarinho.

Another Brazilian, Allan Do Carmo, finished fourth for the second year in a row, agonisingly missing out on a medal by just five hundredths of a second.

It was so close at the end that his position had to be determined by video review.

The winner Schouten said the race panned out differently from what he is used to.

"Normally, I'm always in the back of the pack, waiting till the last three K," said Schouten.

"But the pace was really slow, so I thought maybe it's possible to break away.

"It wasn't, so I was still waiting."

The finish in the women's race was equally, or perhaps more, dramatic.

Cunha and Samantha Arevalo led a four-woman break on the final lap, swimming side-by-side.

Horner and Jungblut, the other two in the group, swam so close together it prompted five whistles from the referees urging them to separate.

Eventually the race was decided simply by who was faster touching the finishing pad.

"It was a slow race, so I tried to do a different race after the third lap, but the other swimmers caught me and slowed it down again," said Cunha.

The next event on the World Series Calendar is at Canada's Lac Megantic in Quebec on August 11.