A stone-cold putter cost the Masters champion as he missed numerous opportunities on the Southport links and ran up six bogeys.
He repaired some of the damage with four birdies, including on the 18th, and having faced the most difficult conditions of the first day before finishing at 8.43pm, the Masters champion believes he can bounce back.
"There were just too many stupid mistakes but every time I made a stupid mistake, thankfully I made a birdie to sort of keep myself in it," said McIlroy, who's seven shots behind leader Jackson Suber.
"I'm not too far away. If you look at the discrepancy between the scoring this morning and the scoring this afternoon, it looks like that's going to be flipped tomorrow with the conditions again.
"Hopefully, I can take advantage of the more benign conditions in the morning and shoot one under par and get back in it."
McIlroy missed three putts from inside four feet and was 104th in the putting statistics.
And he was literally brought to his knees at the par-five 17th where, after hooking his approach into the gallery and then flying the green into a bunker, he contorted his stance to splash out to eight feet - only to miss for a bogey.
He at least finished on a positive with a brilliant approach from 198 yards to five feet and finally sank a short birdie putt.
McIlroy will have to defy recent history to recover and claim a second Open title and seventh major overall, which would officially make him the most successful European golfer of all-time.
Although he did win last year's Masters from seven shots back, each of the last 26 Open champions have been within five of the lead after round one. The last player to come from further back was Mark O'Meara in 1998 although, interestingly, that was at Birkdale.
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