In the men’s 100m, first round, Justin Gatlin, second in his heat with 10.16 and Christian, 10.29, easily made progress.
Isiah Young, however, recorded the day’s fastest time of 10.14. Michael Rodgers, 10.24, also booked his semi-final ticket.
On the women’s side, Dezerea Bryant led the way with 11.25. English Gardner, 11.28, was the only other woman under 11.3.
Sha’Carri Richards, who is the fastest American this season with 10.75, also qualified for the semi-final round with 11.41.
Antiguan-born Rai Benjamin, 49.61, Amere Lattin, 49.66, Kerron Clement, 49.79 and TJ Holmes, 49.87, were the fastest qualifiers from the opening men’s 400m hurdles round.
Allyson Felix, running her first race since giving birth, squeezed into the semi-finals of the women’s 400m after finishing fourth in heat one. Felix’s time of 52.20 placed her behind Lynna Irby, 51.14, Kaylin Whitney, 52.02 and Briyahna DesRosiers 52.02.
“I’m grateful to be back racing,” said Felix. “Even though it wasn’t a great result for me, it’s a starting point. My biggest goal is next year. And I know that I’m capable. Now I have time on my side and I can get where I need to go.”
Shakima Wimbley, however, ran the day’s fastest time of 50.87 while Courtney Okolo is next with 51.10.
Phyllis Francis, who is the defending champion with a bye, will only contest the women’s 200m.
Two men, Trevor Stewart, 44.76 and Michael Norman, the one to beat, 44.81, went sub-45 in the one-lap event. Fred Kerley was the third fastest on the day with 45.09.
Keturah Orji won the women’s triple jump title with 14.56m while Sam Mattis threw 66.69m to take the top spot in the men’s discus.