Kenya’s Faith Kipyegon, winner of the last two Olympic 1,500m titles, looked in great shape to bid for her first world title as she cruised through the first round of qualifying on Friday.
Kipyegon, who picked up a world silver in Doha in 2019 a year after having a baby, came to Eugene on the back of posting the year's fastest time on the same Hayward Field track.
That was a scorching three minutes, 52.59, and though she did not need to go anywhere near that on Friday her 4:04.53 winning time was still lively for a heat.
The 28-year-old hit the front 600m out, staying clear of any potential trip risk in a crowded lead group, then cranked up her trade mark, almost imperceptible, acceleration to forge clear while still looking in total cruise mode.
Ethiopian Gudaf Tsegay, second in the world this year, led home the third group in 4:02.68 - the fastest time of the night.
Another Ethiopian, 21-year-old Hirut Meshesha, third fastest in the world this year, and British Tokyo Olympic silver medallist Laura Muir were the breakaway two in the opening heat.
Kenya's Winny Chebet also qualified for the women 1500m semifinal after coming second in heat 3.
The semi-finals are on Saturday ahead of the final on Monday.