The Northern Irishman was two under going into the back nine, but a run of five bogeys in the last six holes saw him card a two over par round of 74, leaving him eight shots behind overnight leader James Kingston from South Africa.
McIlroy, who spends much of the year on the PGA tour and owns a $10m property in Florida, said the unseasonal weather – with temperatures failing to hit double figures all day and play being halted for 90 minutes due to the risk of lightning – affected his round.
“It was one of those rounds that I let slip through my fingers,” said the 22-year-old, still chasing his first win of the year. “Even when I was three under I thought things could have been better.
“My hands were cold, I was wearing mittens all the way round, trying to keep them warm. But I’m pretty unfamiliar with these conditions after playing in warmer climates.”
Playing partner, and compatriot, Graeme McDowell also finished two over par, following a consistent round that ended disastrously with a double bogey at 18, after finding the water surrounding the raised green.
Further back in the field, reigning champion Luke Donald endured a torrid day, as he carded a six over par round of 78, to leave him in danger of missing the cut at the end of round two.
The world No6 shot four bogeys and a double on the front nine, but regrouped to drop just one additional shot in the second half of his round.
At the top of the leaderboard, Finland’s Mikko Ilonen birdied the 14th, 15th and 18th to finish one shot behind leader Kingston, yet still voiced similar complaints to McIlroy.
“It was pretty nippy and we had some hail as well,” he said. “All day I was thinking ‘can I get these waterproof trousers off?’ but I couldn’t. This is the British summer time.”
Scotland’s Scott Henry is two shots off the lead, tied for third place, alongside Spain’s Gonzalo Fernandez-Castano and Martin Wiegele of Austria, who resumes his first round this morning having only completed 13 holes before play was suspended shortly before 9pm due to bad light.
-6: James Kingston
-5: Mikko Ilonen
-4: Gonzalo Fernandez-Castano
-4: Scott Henry
-4: Martin Wiegele (after 13 holes)
-3: Matteo Manassero
-3: George Coetzee
-3: Thomas Bjorn
-3: Simon Khan
-3: Marc Warren
-3: Alejandro Canizares
-2: Lee Westwood
Level: Sergio Garcia
+2: Rory McIlroy
+2: Graeme McDowell
+6: Luke Donald