Australia has claimed its first swimming gold medal at the World Aquatic Championships in Doha, clinching a nail-biting win in the 4x1500m mixed open-water event.

The team of Moesha Johnson, Chelsea Gubecka, Nicholas Sloman and Kyle Lee held off a fast-finishing Italy to win in the Qatari capital.

Western Australian Lee touched in a time of one hour, three minutes and 28 seconds to just pip the defending-champion Italians (1.03:28:20), with Hungary (1.04:06:80) claiming bronze more than 28 seconds behind.

Hot favourites France finished sixth, behind Germany and the United States.

Zimbabwe-born Lee, who took an accountancy examination in his Doha hotel the day before the race, said it was important he held his nerve at the finish.

"I just tried to stay calm and it is so hectic in that finishing shoot … I guess I got lucky on the touch," Lee said.

"It was so exciting to race today and to know you're not swimming for yourself, you're swimming for your country.

"Everyone swam so well so going into the water, they were wishing me the best of luck and I tried to do my best for them."

Australia's victory comes a day after 25-year-old Gubecka picked up silver in the 5km open-water race, narrowly beaten after a thrilling duel with Dutch superstar Sharon van Rouwendaal.

The mixed relay success was Australia's second gold of the world titles after Alysha Koloi took out the women's 1m springboard event.

AAP