McIlroy was two under par after six holes at Le Golf National but eventually had to settle for a level-par 71 featuring four birdies, four bogeys and two trips to the water at the 2018 Ryder Cup venue.
That left the 27-year-old five shots off the lead held by Denmark’s Lucas Bjerregaard, whose 66 gave him a one-shot lead over defending champion Bernd Wiesberger, Belgium’s Thomas Pieters, Thailand’s Thongchai Jaidee and Spain’s Adrian Otaegui.
McIlroy has been putting in the hours on the range with coach Michael Bannon ever since an opening 77 in the US Open led to a first missed cut in a major championship since the 2013 Open.
And asked what areas he was working on, the four-time major winner joked: “Have you got 10 minutes?
“My left-hand grip is too strong. Takeaway was going on the inside. Wasn’t holding my right elbow properly at the top of my swing. Wasn’t getting my right knee out of the way on the downswing... I’ve been working on a few things.
Despite his problems, McIlroy still fared better than Masters champion Danny Willett, who double-bogeyed the 18th after finding water with his approach to card a 75 while two-time winner Graeme McDowell slumped to a nine-over-par 80.