Mahut's 4-6, 6-4, 7-5 defeat of Finland's Jarkko Nieminen earns him the thrill of playing top seed Juan Carlos Ferrero in the second round.
"That win means I don't have to play next week (in a challenger tournament). I've already booked my place in the Australian Open draw," said Mahut, who hopes a right leg injury will not hamper him against the world number one.
Two French youngsters, whose careers appear in danger of stalling after a fine 2002, Richard Gasquet and Paul-Henri Mathieu, lost after being in control of the first set.
Gasquet, 17, wasted six match points in a second set tiebreak against Gaston Gaudio of Argentina before going down 1-6, 7-6, 6-4 while Mathieu held three set points before losing 7-5, 6-4 to Morocco's Hicham Arazi.
It was Mathieu's first appearance in the Bercy stadium since he lost the final match of last year's Davis Cup final against Russia after being two sets up against Mikhail Youzhny.
The 21-year-old, whose spirit was almost broken by his Davis Cup trauma, has had a terrible year and the defeat by Arazi was his 14th first round loss this season.
Mathieu feels he has aged 10 years in the past 11 months. "I thought I had a tough skin but I realise now it wasn't thick enough," he said.
French qualifier Gregory Carraz beat Czech Radek Stepanek 2-6, 6-2, 7-6.
Britain's Tim Henman thumped Russian Nikolay Davydenko 6-3, 6-4 to book a second-round showdown with his 2003 nemesis Sebastien Grosjean.
Henman, who is determined to end a frustrating year in style, has been beaten by Grosjean twice on his favourite grass surface this season, including in the Wimbledon quarter-final.
The Frenchman needs to win the title here to have any chance of earning the final spot in the season-ending Masters Cup.
"This is a good opportunity to get revenge on his home turf," said Henman, whose season has been hobbled by surgery to his right shoulder.
"There is a lot more at stake for him than me and I have got to take advantage."
Spain's Albert Costa, French Open champion last year, also reached the second round of the final Masters event of the year, beating Argentina's Mariano Zabaleta 6-7, 6-4, 7-5.
