The former Ryder Cup star bogeyed the second on the Retz Course but followed that with a hattrick of birdies.
That saw the World Number 92 - seeking a first European Tour title since 2007 - move to two under par.
Six players were on three under during the early exchanges - and like Hansen - Scot Andrew McArthur and England's James Morrison were playing the Retz Course.
Hansen's compatriot Jeppe Huldahl, Swede Martin Erlandsson and English duo Gary Clark and David Dixon had all made promising starts on the Marly Course.
But the news was not so good for Sweden's Peter Hanson, who withdrew with a chest infection from his final event before he makes his Ryder Cup debut.
The Czech Open champion decided not to tee off in Paris and instead pulled out in order to be fully recovered for The Celtic Manor Resort next week.
Hanson had said on the eve of the event: "I was feeling okay up until yesterday. I got a bit of a chest infection, a bit of a cold. I have a little bit of fever.
"I'm a little bit worse today, so not ideal the way I want to prepare this week. But like Colin said, we don't want to be sick next week, so I'll try to treat that and see the doctor.
"There's a lot of colds and stuff going around. Hopefully I will be ready Monday.
"If I feel as bad it's no point being out here and wasting all of that energy instead of trying to feel better and fresher come next week."
The first two rounds at Golf de Joyenval are in a pro-am format and Padraig Harrington - hoping to find some winning form ahead of next week's Ryder Cup - was playing with his brother Fergal.