Britain's Shanaze Reade opened her campaign for BMX gold by qualifying fifth fastest in the opening time trial.
Australian time trial world champion Caroline Buchanan went fastest, with a lap of 38.434 seconds, almost a full second better than Reade's.
Crewe rider Reade, 23, has been allocated starting gate three in the first of Friday's semi-final races.
In the men's time trial, Britain's Liam Phillips was 12th fastest.
Dutchman Raymon van der Biezen leads the standings, with the men's competition due to resume with the quarter-finals on Thursday.
"It felt quite good out there. The first race is always going to be a bit rusty," said Reade.
"I have been sitting around and watching Olympic titles being won and have just wanted to get out there and compete myself."
Reade narrowly missed out on the Olympic title four years ago when she crashed attempting a daring late overtake in the final run.
After an injury-hit season this year, her time of 39.368 seconds was faster than French world champion Magalie Pottier.
Buchanan, who earlier in the week voiced suspicions that Reade had enjoyed preferential access to the course, will line up in the same semi-final as the Briton after a slick run brought her home 0.21 seconds clear of the second-placed Sarah Walker.
Meanwhile, Phillips briefly held the lead before dropping down the pecking order, with Australian Sam Willoughby, who won the world title for the first time in May, sixth quickest.