Nia Ali of the United States, defending world champion in the event, fell out of contention at Hayward Field after catching her trailing foot on the ninth barrier while leading, before soon afterwards Alysha Johnson stuttered over the first hurdle and failed to clear the second.

It was a huge contrast for a home crowd that has previous witnessed two home sprinting clean sweeps in the men’s 100 and 200m.  

Ali, 33, has returned to action this season after having a daughter with her second husband, Canada’s Olympic 200m champion Andre De Grasse, and had a wildcard thanks to the gold she earned in the steamy heat of Doha three years ago.

But her defence was over almost as soon as it had begun as what looked like an imminent victory in the opening heat turned into calamity as she hit the ninth hurdle and then the deck after staggering on to the final flight.

"I was running a really good race but I let the speed carry over and I didn’t keep my technique tight enough and lost everything," Ali told the BBC, adding rather poignantly that all her family were trackside to watch her.

Worse was to follow as Johnson, the only athlete to have beaten Puerto Rico’s Olympic champion Jasmine Camacho-Quinn in the last two years, stuttered in front of her first hurdle as if she had never faced such a challenge before, and her race was done.

Normal service was resumed by the two remaining home 100m hurdlers as world record holder and Olympic silver medallist Keni Harrison won in 12.60 seconds and Alia Armstrong clocked 12.48, just 0.01 off the personal best she set at the US Championships.

The latter was the second fastest time of the day behind the African record of 12.40 set by the exuberant Tobi Amusan of Nigeria, who missed a medal by one place at last year’s Olympics but looks all set to reach the podium in Eugene - barring accident.

Meanwhile Camacho-Quinn qualified third fastest in 12.52 after a tentative start, although in her rather subdued trackside interview she referred enigmatically to "some issues" that she would have to "work through."

Jamaica’s Olympic bronze medallist Megan Tapper was ninth fastest in 12.73.

There were no excursions or alarms for the defending world champion in the women’s long jump qualifying, however, as Germany’s Olympic gold medallist Malaika Mihambo surpassed the automatic qualifying mark of 6.75m for tomorrow’s final with an opening effort of 6.84m, the second best of the session.

Home jumper Quanesha Burks topped qualifying with 6.86m with Nigeria’s world and Olympic bronze medallist Ese Brume on 6.82m, Ukraine’s 2019 world silver medallist Maryna Bekh-Romanchuk on 6.81m, Khaddi Sagnia of Sweden on 6.78m and Australia’s Brooke Buschkuehl on 6.76m also qualifying automatically.

Meanwhile Canada’s Olympic and world indoor champion Damian Warner made a strong start in his bid to earn a first world decathlon title at the age of 32 as he established a 90-point lead after a day nine morning session involving two of his best events, the 100m and long jump, and the shot put.

Warner moved on to the evening session’s high jump and 400m on 2846 points, with Zachery Ziemek of the United States on 2756 and Puerto Rico’s Ayden Owens-Delerme on 2728.

Warner’s team-mate Pierce LePage, the Commonwealth silver medallist, was three points behind in fourth place, one ahead of France’s world record holder Kevin Mayer, right Achilles tendon heavily taped, who performed well enough in the opening two events but failed to deliver a shot put close to his best of 17.08m, only managing 14.98m.