Australia's Jarrod Poort finished fifth in 5km open water race at the world championships in Barcelona on Saturday.
Poort clocked 53min 34.3sec to trail Tunisian Oussama Mellouli who won in 53:30.4.
Canadian Eric Hedlin was second (53:31.6) followed by Thomas Lurz of Germany (53:32.2).
Olympic champion Mellouli surged ahead as soon as he got within the ropes outlining the finish area.
"I was hoping they wouldn't stay with me," Mellouli said.
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"Once I put the jets on I was able to take off, finish the race and take the win."
Lurz had previously won the 5K title seven consecutive times but he couldn't match Mellouli's sprinting.
"It's OK, I'm 33 years old and I started working again in January," Lurz said
"I knew in the last 50 metres I would not win. (Mellouli) swims the 100 free five seconds faster than me or more. This is the problem."
US swimmer Haley Anderson won the earlier women's race to take the first gold medal of the meet.
Anderson finished in 56:34.2 ahead of Brazilians Poliana Okimoto (56:34.4) and Ana Marcela Cunha (56:44.7).
Of the Australians, Danielle DeFrancesco finished 11th and Bonnie Macdonald 14th.
The races took place in ideal conditions, with the water 24C and the air temperature between 28 and 29C.
