Muskerry's Niall Gorey was forced to retire but Portmarnock's John Greene survived 100F temperatures to lead the Irish survivors in the European Mid-Amateur Championship in Madrid.
The former South of Ireland champion opened with a seven-over-par 79 at a tiger tough Puerta de Hierro as Muskerry's Dave O'Donovan posted an 82.
Six over through the turn in the Spanish capital, Gorey withdrew after 11 holes citing heat exhaustion as dizziness made it impossible to go on.
"I wasn't very well yesterday either and only played 13 holes in practice," Gorey said. "I thought I was okay today but had to stop or I'd have been in trouble."
The Irish have a battle on their hands when it comes to making the cut for the top 60 and ties after a day that saw just three players in the 140-strong field break par.
Greene opened with three straight bogeys but birdied the last to share 52nd with a 79 as O'Donovan made just one to share 92nd and may need a score in the mid to low 70s to shuffle up the leaderboard
Denmark's Morten Bo Knudsen, Sweden's Erik Persson and Puerta de Hierro's member Bernardo Campos shot one-under-par 71s to lead by one shot from François Illouz as the field average 80.28.
"The course is very difficult," Gorey said. "The greens are like lightning and extremely undulating."