Kerley, who won silver in the 100 metres at the Tokyo Olympics, stormed to victory with a meeting record in lane five, using his long strides to his advantage in the final few metres and giving Simbine (9.99) and Omanyala (10.05) no chance of catching him.
"I can't describe my happiness for winning this race and hitting the meeting record today," Kerley said.
"This is the result that I was expecting and I will keep up to achieve and reach the World Championship in the best shape ever."
Olympic gold medallist Lamont Jacobs did not compete due to a back issue.
American Shamier Little won the women's 400m hurdles in 53.95, while her compatriot Grant Holloway finished second behind Rasheed Broadbell in the 110m hurdles.
"I am not happy about my performance today. My goal was the first place. The crowd was very loud and they got me distracted," Tokyo silver medallist Holloway said.
"I'll work harder now to get ready for the upcoming competitions especially the World Championship where my goal is to achieve the gold medal."
In the final event of the night, home hero Soufiane El Bakkali won the 3,000m steeplechase to the delight of the home crowd.
Olympic champion El Bakkali ran a personal best of 7:56.68 - the fastest time this year - to finish well ahead of Getnet Wale (8:05.15) and Abraham Kibiwot (8:05.51).
MAHUCHIKH, MORAA WIN
Ukraine's Yaroslava Mahuchikh and Kenya's Mary Moraa, reigning Diamond League champions in the women's high jump and 800 metres, claimed wins in their respective events.
Mahuchikh took victory with an effort of 2.01 metres. The Tokyo Games bronze medallist beat compatriot Iryna Gerashchenko, who managed 1.91.
Moraa clocked a time of 1:58.72 to finish ahead of Australia's Catriona Bisset in second and American Sage Hurta-Klecker in third.
