In his French Open debut, Kevin Stadler shot a bogey-free 7-under 64 to lead by a stroke after the first round on Thursday.
The American golfer, who won the Phoenix Open in February and shared eighth place at the Masters in April, made seven birdies on a punishing golf course that will host the Ryder Cup in 2018.
Marcel Siem of Germany was in second place, one stroke clear of Stephen Gallacher of Scotland. Jamie Donaldson of Wales and Felipe Aguilar of Chile were tied for fourth at 4 under.
Defending champion Graeme McDowell (70) and U.S. Open champion Martin Kaymer (72) stayed in contention while Padraig Harrington (74), Thomas Bjorn (76) and Victor Dubuisson (76) will need a good performance in the second round on Friday to make the cut.