Chepkoech, 27, broke the previous record mark of 8 minutes 52.78 set by Bahrain’s Ruth Jebet in 2016 and, after breaking clear 2,000 metres into the race, she finished 16 seconds clear of her nearest rival.
“I am so grateful,” Chepkoech told reporters. “I said from the beginning, from the first lap, and I was watching the time, and I knew I was going to break the world record.”
Her previous best was 8:59.36 in Paris last month and she finished fourth in the 2016 Rio Olympics and 2017 London world championships.
American world silver medallist Courtney Frerichs took second in a North American record of 9:00.85.
“That race was incredible,” Frerichs said. “Eight seconds under the world record. It’s such a huge step for the event.”