Phil Healy and Molly Scott both missed out their respective finals at the World Indoor Athletics Championships in Belgrade.
Scott was the first Irish competitor on track and finished fifth in her 60m heat in a time of 7.26, just short of her personal best and good enough to progress to the semis.
She ran even quicker time in her semi-final heat - 7.23 - but finish seventh, which was not enough to get her through.
"I came here to PB so I'm disappointed," Scott told RTÉ Sport afterwards.
Healy shook off a bout of Covid-19 last week to win her 400m heat, finishing in a time of 51.75 to ensure her progression to the semi-final in style.
The Cork woman revealed that at one stage she was contemplating withdrawing from the 400m event after a disappointing session on Tuesday as she attempt to shake off the effects of Covid.
She was sixth in her semi-final run, and later reflected: "That race just shows the joys of indoor racing - it's messy. Once you're in a semi you want to get to the final but it wasn't to be. I'll take a rest tomorrow and come out for the relay on Sunday."
Mark English also tested positive for Covid last week but wasn't able to shake off the effects as well as Healy and finished fifth in his 800m heat and was well off the pace with a time of 1:51.35.
"It was a tough race," said English afterward. "I haven't had the right preparation coming into this, I had Covid last week. I thought I was able to go out and run but it just proved a little bit too much out there.
"My aerobic development just wasn't where it needed to be and I think it showed out there."
There was disappointment elsewhere as Sarah Healy finished fifth in her 1500m heat in a time of 4:12, narrowly missing out on qualification.
Sophie Becker was fourth in her 400m heat, but her time of 53.47 was off the qualifying pace.
Darragh McElhinney was the last of the Irish competitors out in the heats and he was unable to progress to the semi-finals.
The European Cross Country silver medalist finished a disappointing ninth in his 3000m heat in a time of 8:06.31.