Ellen Walshe finished eighth in the 200m butterfly final at the World Aquatics Championships in Singapore.
The 23-year-old Templeogue swimmer finished third in her semi-final but found the pace in the closing 50m too much in a final where Canada's Summer McIntosh came within 0.18 of a second of breaking the world record - winning in 2:01.99.
Walshe was in the mix for a medal position through the first 150m but tailed off in the final length, eventually finishing in 2:08.34.
The United States' Regan Smith took silver, Australia's Elizabeth Dekkers in bronze and a mention for China's Zidi Yu in fourth, who is just 12 years old.
Walshe, who was a finalist in the the 200m individual medley earlier this week, had brought the 200m butterfly back into her repertoire for the first time in five years earlier in 2025.
"I think even if I was to go back and think I'd be in that final, I would have been like, absolutely not, but I guess expectations build as you are a competitor, but yeah, it's just a poor performance tonight," said Walshe, who will now turn her attention to 400m individual medley on Sunday, which is her main event.
She added: "I think the important thing now is just to recover and wait to see what happens on Sunday. It's a big heat ahead, I think going in heat two, and it's quite stacked, so it'd be interesting to see how it goes."
Ellie McCartney is through to Friday's 200m breaststroke final after a tremendous swim in her semi-final, finishing third in a time of 2:23.79 behind Olympic champion Kate Douglass of the United States.
The Enniskillen swimmer, who claimed gold at the Under-23 European Championships in June, has qualified sixth fastest overall, improving on her time of 2:25.22 from the heats.
"I'm ecstatic. This is what we train for, we train to perform in the heats, make it through the semis and progress through the rounds," she said.
"And I think that's really been a strength this year that I've been able to progress through each of the rounds. So, to make it to a World Championship final in my first Worlds, it's really exciting. I think here it's just been so unpredictable.
"You get top two, top three in a semi-final and you're not guaranteed a final, so it's important that you just put your best foot down and whether or not I made the final, I would be able to walk away satisfied just because I put my best foot forward and PB'd, I know I've left everything in the pool."
John Shortt has missed out on a place in the men's 200m backstroke final after finishing 15th overall in the semi-finals.
The 18-year-old Galwegian recorded a time of 1:57.30 to finish seventh in his semi-final heat, which was slightly slower than the 1:56.98 he set in the morning heats, and which in turn was just shy of the Irish record of 1:56.61.
"Just wasn't as fast as I would have liked it, but you know what? It's been a really long summer already, so to be going my third best time or whatever it is, I really cannot be too angry at myself for that," he said.
Shortt will return to action on Friday for the 4x200m freestyle relay alongside Evan Bailey, Cormac Rynn and Jack Cassin.
There was disappointment for Eoin Corby in the men's 200m breaststroke, clocking a time of 2:11.84 and finished 20th overall, four spots outside the qualifying places.
Corby said afterwards, "I'm a bit disappointed. I gave it my best shot. I was a small bit off my PB. It’s a bit annoying that my PB would have made it back, but yeah, I just need to come back better next year."
In the 100m freestyle Danielle Hill touched in 56.59 seconds, finishing 37th overall and well outside the qualifying places.
The Larne swimmer returns to the blocks on Friday for her main event, the 50m freestyle, an event she holds the Irish record in, in 24.68.
Jake Passmore placed 27th overall from 66 divers in the 3M Springboard Preliminaries.
The 2024 Olympian was just 14 points outside the top 18 places required for the semi-final with 360.60 points. Nonetheless, Passmore was satisfied with his performance in the context of a difficult year in which he has been ruled out of action for six months due to shoulder surgery.
"Overall, can't complain today," Passmore said. "Not the best performance but I’m really pleased that despite the difficult year I’ve had, I’ve managed to stay competitive."
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