Dutch ace Ellen Van Dijk successfully defended her time-trial crown at cycling's road world championships on Sunday for her third career title, outpacing Australia's Grace Brown and European champion Marlen Reusser.

The 35-year-old was the final rider down the ramp and chased down Brown's blistering early pace to win by 12.73 seconds in 44min 28.60sec and clinch another title, having also won in 2013.

Switzerland's Reusser was third, 41.68 sec adrift at the opening event of the eight-day road world championships at Wollongong, a coastal city 80 kilometres (50 miles) south of Sydney.

In a major upset, two-time title holder and Olympic champion Annemiek van Vleuten failed to make the podium, with the Dutchwoman managing only seventh, a huge 1min 43.02sec behind Van Dijk.

"I never expected to win. I didn't think it was a perfect course for me but I had a good mental and physical approach with my coach," said Van Dijk.

"I just thought I would give it my all today, a podium spot would be nice, but if it's not, it's not, I still had a great year. I never thought I would win today."

She made a point of not looking at the times set by the other cyclists, instead concentrating on her own riding.

"I wanted to focus completely on myself, but I was so surprised to cross the finish line first," she said.

For the first time at the worlds, women covered the same distance as the men, sharing a 34.2 kilometre (21.2 miles) route running along two laps of a technical and twisting circuit with a small climb.

Commonwealth Games time-trial champion Brown was among the first riders out with her time standing until Van Dijk's exploits.

Reusser appeared on track to challenge Brown after setting a faster pace through the first split, but faded as Van Dijk, who was following her, rose to the challenge.

"It was a very long and nervous wait," said Brown. "I thought there was still a chance I could win the race overall, but Van Dijk had a phenomenal day. She's a seasoned time-trialer and she deserved the win."

In another first, under-23 women competed for their own championship as part of the same race with Italy's Vittoria Guazzini, who finished fourth 52.11sec behind Van Dijk, taking the U23 gold.

The men's time trial is later Sunday with Italy's Filippo Ganna the two-time defending champion.