Nick Sloman has become the second Australian open water swimmer in the space of two days to just miss out on a medal at the world aquatics championships in Doha.

In the best shape of his career, Sloman was right in the thick of the battle for the podium in a thrilling finale in old Doha port on Sunday before eventually touching in fifth place just four-tenths of a second away from nicking his first individual global medal.

But just like Moesha Johnson 24 hours earlier in the women's race, Queenslander Sloman's substantial consolation in a race won by Hungarian Kristof Rasovsky was to seal his place at the Paris Olympics.

With Kyle Lee also touching in ninth place, it meant that the Dolphins for the first time could celebrate the qualification of a full contingent of four open water swimmers for the Paris Games.

"I know what it's like to miss out after Tokyo so there was no way I was going to let this chance pass," said 26-year-old Sloman, a bronze medallist in last year's world team event in Fukuoka.

"It hurt, particularly when the pace picked up in that final lap, but I knew I had to stay in touch with the leaders."

While Rasovsky, who'd previously won the world 5km event in 2019, forged away over the final 400m from Marc-Antoine Olivier in the final sprint for gold to win in 1 hour 48min 21.20sec, a clear 2.4sec ahead of the Frenchman, there was an almighty scramble for the bronze.

Britain's Hector Pardoe ended up winning the minor medal in 1:48:29.20 but just behind him came another six swimmers all finishing within the space of two seconds, including Sloman (1:48:29.60) and 21-year-old Lee (1:48:31.20).

"I just can't believe it," said a delighted Lee, who emigrated to Western Australia from Zimbabwe with his family when he was six.

The Aussie swimmers' Games selection has to be ratified by the Australian Olympic Committee, but it seems certain the Doha trio will join last year's world 10km silver medallist Chelsea Gubecka, who was in the stands cheering her teammates, in the Paris-bound squad.

After two medal days for Australia in the diving pool, the team plunged back down to earth on Sunday when Kurtis Mathews and Samuel Fricker could only finish 20th in the 3m synchronised final.

Wang Zongyuan and Long Daoyi took the title with a dominating display for China, winning with 442.41pts, a huge 58.17 points clear of Italians Lorenzo Marsaglia and Giovanni Tocci. The Aussie pair scored 311.61.

Australian Melissa Wu qualified for the semi-finals of the 10m platform with the eighth best score, but teammate Nikita Hains couldn't get through qualifying.

In the first clash of their programme in group C, Australia's water polo women enjoyed the easiest of workouts in a 32-1 thrashing of Singapore.