Sycerika McMahon and Barry Murphy have missed out on progressing from their heats at the World Swimming Championships in Shanghai.
16-year-old Down swimmer McMahon, competing in her first World Championships, finished third in her 400m freestyle heat in a time of 4 minutes 16.44 seconds. That gave her an overall ranking of 24th place with only eight swimmers progressing to the final.
McMahon is the European Junior champion in the event and won the gold medal at the European Junior Swimming Championships in Serbia a couple of weeks ago.
Double Olympic Champion Rebecca Adlington struggled to qualify, finishing third in her heat and seventh overall, but later claimed a silver medal behind Italian defending champion Federica Pellegrini (4:01.97). Camille Muffat of France took bronze.
In the 100m breaststroke, Murphy was seeded 20th but had a disappointing swim and his time of 1:02.50 was almost two seconds slower than the personal best he swam earlier this year in Indianapolis.
Afterwards, Murphy felt his "taper", the period of lower intensity training prior to a major race, was too long.
He said: "The whole race just didn’t feel very good, I felt low in the water from the start and I didn’t have that pop that I usually have. It was pretty disappointing. I’ve changed some things around this year training wise and I did a longer taper than usual for this meet.
"Maybe it’s not what suits me right now. I was pretty psyched [before the race] and obviously I’ve been waiting a long time for this meet to come around. After that time in March I was really excited, but I guess it just didn’t work out."
National Performance Director for Swim Ireland Peter Banks said: "There is no doubt Barry was disappointed. He is going to look back at his taper and maybe it was longer than he needed.
"Sycerika’s 400m freestyle was a best morning swim and it was a good experience for her learning how to deal with swimming at a major Championship like this – a positive start overall for Sycerika."
The meet continues for seven more days and both McMahon and Murphy have more swims to race.
Irish swimmers in action tomorrow on day two of competition are McMahon in the 100m breaststroke, Melanie Nocher in the 100m backstroke and Gráinne Murphy in the 1500m freestyle.
Heats gets underway tomorrow morning at 90am local time, which is 2am Irish time.