Australia's Caroline Buchanan underlined her gold medal credentials in the BMX at the London 2012 Olympic Games by dominating the women's seeding run.
BMX is making its second appearance at the Games, following a successful debut in Beijing four years ago.
In front of a packed-out stadium Buchanan thundered out of the eight-metre high start ramp to complete the 440m long circuit in a time of 38.434sec.
New Zealand's Sarah Walker was second in 38.644, with Colombia's Mariana Pajon third in 38.787 from the field of 16 starters.
Laetitia Le Corguille was the fastest of the two French medal contenders, the Beijing silver medallist finishing fourth in 38.976 just ahead of Britain's gold medal hope Shanaze Reade who clocked 39.368 for fifth.
Fellow Frenchwoman Magalie Pottier, the reigning world champion, was seventh in 39.778.
American Brooke Crain found trouble on one of the final bumps leading to the finish, crashed and took a few moments before crossing the line on her bike. She will be allowed to continue.
The seeding run determines the seeding and gate selection order for the first run of the quarter-finals and the gate selection order for the first run of the semi-finals.
With only 16 participants, the women's field now splits into two semi-final heats of eight riders. Each heat completes three separate runs on the course and the top four riders from each heat after the three runs qualify for the final.
Buchanan is in heat one containing Le Corguille, Reade, American Alise Post, fellow Australian Lauren Reynolds, Stefanie Hernandez of Venezuela, Latvian Sandra Aleksejeva and Brooke.
Walker is in heat two with Pajon, Dutchwoman Laura Smulders, Pottier, Czech pair Aneta Hladikova and Romana Labounkova, Lithuanian Vilma Rimsaite and Brazilian Squel Stein.
The men's and women's finals will also be held on Friday.
Women's BMX seeding run
1 Caroline Buchanan (AUS) 38.434sec
2 Sarah Walker (NZL) 38.644
3 Mariana Pajon (COL) 38.787
4 Laetitia le Corguille (FRA) 38.976
5 Shanaze Reade (GBR) 39.368
6 Laura Smulders (NED) 39.420
7 Magalie Pottier (FRA) 39.778
8 Alise Post (USA) 39.890
9 Lauren Reynolds (AUS) 40.045
10 Aneta Hladikova (CZE) 40.846
11 Romana Labounkova (CZE) 41.096
12 Stefany Hernandez (VEN) 41.253
13 Sandra Aleksejeva (LAT) 41.752
14 Vilma Rimsaite (LTU) 42.162
15 Squel Stein (BRA) 42.995
NR Brooke Crain (USA) DNF