Javier Ballesteros looks certain to miss out on the matchplay stage of the British Amateur Championship after opening with an 81 at Royal Portrush.
Ballesteros, the 23-year-old son of the late Seve Ballesteros, was 15 shots behind English leader Daniel Brown after his 11-over-par round.
England's Ryan Evans and Scotland's Liam Johnston were among the leaders at nearby Portstewart on 68.
Moyola's Chris Selfridge is on course to qualify after a 69 at Portstewart.
Naas's Jack Hume was the leading Irish player at Portrush on 69, with last year's Irish Close champion Cormac Sharvin, from Ardglass, also well placed after a level-par 70 on the Dunluce course.
Greystones player Paul Dunne and Tullamore's Stuart Grehan both managed one-under 70s at Portstewart, but Northern Irish hopefuls Reeve Whitson, Harry Diamond and Tiarnan McMahon are all struggling after their opening rounds.
Last year's Spanish Amateur Open champion Whitson fired a 75 at Portrush, with Belvoir Park's Diamond only managing a 78 at the same venue and McMahon carding an 80 at Portstewart.
Of other Northern Irish competitors, Belvoir Park's Gareth Lappin joined Whitson on 75 at Portrush while Royal Portrush member Jamie Richardson shot a 76 at Portstewart.
Italian Renato Paratore, who is 15th in the world amateur rankings, shot a level-par 71 at Portstewart with Belgium's highly-rated Thomas Detry hitting a 73 at Portrush.
After three opening pars, Ballesteros, the 2012 Madrid Amateur Open winner, had five bogeys in six holes from the fourth hole on the Dunluce links.
Following a double bogey at the 10th, Ballesteros managed his only birdie of the day on the 13th but he finished in hugely disappointing fashion as bogeys on the 16th and 17th were followed by three more dropped shots at the last.
The top 64 players will qualify for Wednesday's opening matchplay round after Tuesday's second round of strokeplay.
Currently, 63 players are one over or better.
The event began in Northern Ireland on the day it was confirmed the Open Championship will return to Royal Portrush, possibly as early as 2019.