Rhasidat Adeleke finished fourth in her first outing over 400m this season - a stacked event at the Oslo Diamond League.
The 22-year-old continues her preparations for the World Championships in Tokyo this September, crossing the line in a time of 50.42 seconds.
In a highly-competitive race, the Dubliner was edged out of a top-three finish in a race where American Isabella Whittaker (49.58) and Norway’s Henriette Jaeger (49.62, national record) both went sub-50.
It was a dramatic finish at the front as Whittaker chased down the home favourite down the stretch.
World Indoor champion Amber Anning finished just ahead of Adeleke, with Like Klaver (50.64) fifth and Poland’s Natalia Bukowiecka (née Kaczmarek), who edged Adeleke out of the European title in Rome last year and an Olympic bronze medal in Paris, in sixth.
Adeleke, who bypassed the indoor season and delayed her first outing over 400m, returns to action in Stockholm on Sunday for the seventh round of the Diamond League.
In-form Mark English clocked the second-fastest time of his career to finish seventh in the men's 800m.
The Finn Valley man crossed the line in a time of 1:44.33 in a race won by Kenya's Emmanuel Wanyonyi (1.42.78).
Earlier this week, English became the become the first Irishman to break 1:44 in the 800m, lowering his own national record for the second time in 11 days with a brilliant run at the FBK Games in the Netherlands.
In March, the 32-year-old claimed European 800m bronze, a result which now sees him trail only Sonia O'Sullivan in Ireland's all-time medal tally at major championships.
