Ireland's Emily Kay finished 13th overall in the women's omnium having recovered from a huge pile-up crash in the opening scratch race at the Izu Velodrome.
Reigning champion Laura Kenny of Britain was also involved in the incident.
Kay and Kenny, winner in 2012 and 2016 and looking for her sixth Olympic track cycling gold in total, were caught up in the crash near the end of the 30-lap race - the first of four events to decide gold.
At least nine riders were involved in the mayhem with bikes and bodies flying in all directions.
Kenny and Kay were two of four riders unable to finish the race won by American Jennifer Valente who took 40 points. Poland's medal prospect Daria Pikulik also failed to finish.
All those involved in the crash were awarded 16 points.
Kay wore a bandage on her arm for the tempo race and later enjoyed a string elimination race, in which she finished ninth. She ultimately finished in 13th position out of 18 competitors overall on a score of 56 points following the final points race with Valente winning gold.
Japan's Yumi Kajihara took the silver medal and Kirsten Wild of the Netherlands landed the bronze.