The 20-year-old Mathieu saved a match point with an ace in the second set and went on to his second victory in as many career meetings with the 21-year-old Pless. Mathieu became the first qualifier to triumph on the ATP this year, when he defeated Sjeng Schalken of the Netherlands in the final of the Kremlin Cup last Sunday.
"This morning I felt very tired and was hurting everywhere," Mathieu said. "It was hard to bend down to tie my shoelaces. (I'm) Not sure if I would have played this match anywhere else but in Lyon in front of a French crowd. The physician said I was not injured in any way and it was more general fatigue from all of the matches lately."
Brazilian Gustavo Kuerten prevented an All-French final as he defeated Arnaud Clement, 6-4, 6-7 (1-7), 6-3.
"Yesterday against Marat Safin was a great victory and confidence builder for me," Kuerten said. "I think he is one of the most complete players on the tour and to beat him on a fast surface meant a lot to me."
Kuerten also is seeking a second straight title after winning the Brasil Open last Sunday.