Fox posted a time of 101.32sec to beat world champion, Mallory Franklin of Britain, and qualify for the C1 semi-final with the fastest time at the Deodoro Olympic venue.

The Australian had held the title of world champion for three years before Franklin managed to prise it off her last year. 

"I think last year was really disappointing and frustrating," she said.

"But that happens, and it's just about learning and coming back stronger, and I've had a great year this season.

"I've been feeling good, I've changed boats and tried different things so I'm just looking forward to racing here again.

"Last time we came here there was only K1, so now to do both is really nice."

Fox now has a chance of becoming the first slalom athlete to go through a season undefeated, after winning all five World Cup events earlier this year. 

In the men's K1, Ondrej Tunka of Czech Republic qualified fastest with a time of 84.87. 

Olympic gold medallist Joe Clarke would have recorded the fastest time if it wasn't for a gate touch, with the Briton instead finishing third.

The competition continues tomorrow with the mixed C2 finals and the semi-finals in the men's C1 and women's K1.