Cyclist Grace Brown has dominated the women's individual time trial to win Australia's first gold medal at the Paris Olympics.

The 32-year-old, who will retire at the end of this season, clocked 39 minutes and 38.24 seconds over the 32.4-kilometre course in the heart of Paris.

She was a whopping 1:31.59 ahead of British rider Anna Henderson to claim the biggest win of her career.

"I had a plan to pace the race to win gold and I was able to execute my plan, like, pretty much to perfection, if not better," Brown told the Nine Network.

"So, can't ask for a better day."

American defending champion Chloe Dygert was third at 1:32.46 after becoming one of many cyclists to crash in the sodden, treacherous conditions.

Brown is Australia's first gold medallist in road cycling since Sara Carrigan won the women's road race at the 2004 Olympics.

Kathy Watt also won the road race at the 1992 Barcelona Games.

Dygert is the reigning world time trial champion, while Brown won silver at the last two world titles and was fourth in the event at the Tokyo Olympics.

The time trial was contested through the middle of Paris, finishing on the Pont Alexandre III Bridge.

Brown, the 2022 Commonwealth Games champion, had the fastest time check at 13.1km, 5.3 seconds up on Dygert.

That ballooned to 51 seconds at the 22km time check.

Dygert crashed in the second half of the course, coming to grief on a left-hand corner before quickly continuing.

Belgian Lotte Kopecky, the reigning world road race champion, was among the leaders until she also became one of several riders to come to grief and finished sixth.

Brown will also be one of the contenders for the women's road race on August 4.

Until Saturday, the biggest win of her road racing career came earlier this year at the Liège-Bastogne-Liège race.

AAP