Sydney McLaughlin-Levrone's experiment at dropping down to the 100m hurdles ended in defeat on Saturday, with the reigning Olympic 400m hurdles champion finishing fifth at the Philadelphia Grand Slam Track meeting.
McLaughlin-Levrone, who has been unbeatable over her specialist event since 2019, found the going tougher over the shorter hurdles discipline at a rainy and overcast Franklin Field.
The 25-year-old American superstar came home in 12.70sec and never looked like threatening Jamaican winner Ackera Nugent, who crossed in 12.44sec.
Tia Jones of the United States was second in 12.60sec, with Jamaica's Megan Tapper third in 12.66sec.
In other events in Saturday's meeting, Olympic 200m champion Gabby Thomas suffered a surprise defeat in her favoured event, beaten into second place by Melissa Jefferson-Wooden.
Jefferson-Wooden, a 100m bronze medallist at the Paris Olympics last year, stormed home in 21.99sec with Thomas second in 22.10sec.
Tamari Davis took third in 22.59sec, just ahead of Britain's Dina Asher-Smith in 22.65.