Derryman Conor McIlveen finished seventh in his T38 400m heats on the opening day of the World Para-Athletics Championships in Dubai.
The Derry Track Club athlete clocked 58.86 seconds in a race run in 34 degrees centigrade.
McIlveen's task was always going to be difficult with his opponents including Tunisia's world record holder Chida Mohammad Farhat.
In the event, Farhat was pipped by Iraq's Ali Al Rikabi for the heat win.
The Iraqi crossed the line in 53.13 to finish marginally ahead of the Tunisian as they both progressed to Friday's final.
Despite missing out on the decider, McIlveen remained very positive about his first World Championships experience.
"All I can take is the positives of the experience and try and enjoy the rest of it and support the rest of the team," said the 25-year-old Derry athlete.
McIlveen's Derry Track club-mate Jason Smyth will defend his T13 100m title on 13 November with McKillop in action the following day in the T38 1500m.
McKillop will compete in his event along with world championship debutant, City of Lisburn athlete David Leavy.
Glengormley athlete McKillop was forced to miss last year's European Para-Athletics Championships because of injury.
Like Eglinton runner Smyth, McKillop won two gold medals at the last World Para-Athletics Championships in London two years ago but both are only competing in one event in Dubai.
Friday's action will see Galway man Alex Lee become Ireland's first ever blade runner when he races in the T64 200m heats and he will also compete in the T64 100m on Sunday.