The Italian Quick-Step Floors rider was cut adrift of his Australian rival as they entered the finishing straight with 300 metres to go.

Ewan had benefited from a superb lead-out by his Mitchelton-Scott team but then appeared reluctant to fully commit to the sprint, perhaps mindful of a gusting headwind.

Viviani gained a jump from behind before powering past and crossing first in 3 hours 04min 40sec.

It came at the end of a gruelling 121kilometres journey from Glenelg in which temperatures exceeded 40 degrees Celsius.

Germany's Team Sunweb rider Phil Bauhaus snatched second place.

Ewan was forced to settle for third as all the leading riders were awarded the same time.

Ewan does remain in the overall leaders jersey, however, with a 10 second advantage over Viviani.

Another Mitchelton Scott rider, South Africa's Daryl Impey, lies third, 14 seconds behind his team-mate.

Slovakia's Boro-Hansgrohe superstar Peter Sagan remains fifth overall, a further two seconds back, after also crossing fifth today.

Tomorrow is due to mark a 128.2km fourth stage from Norwood to Uraidla.