Brianne Theisen-Eaton has finished the first day of the heptathlon with the lead in the overall standings ahead of Canadian teammate Jessica Zelinka.
The difference between the pair after four events is 195 points, with a dominant display from Theisen-Eaton on Thursday enough to earn her breathing space.
Theisen-Eaton claimed victory in the high jump, shot put, and her 200m heat, with a time of 23.41s giving her a new Games record in the final event of the day.
England's Jessica Taylor managed to remain in third spot for most of the day, but she heads into the second day 419 points behind the leader.
