Dembélé’s firm drive in the 53rd minute came after he was set up by Cornet, who equalized three minutes earlier for Lyon.
Veteran forward Jimmy Briand put Bordeaux ahead in the 15th against his former club.
The win moved Lyon up to sixth place and Dembélé grabbed his 14th goal in 28 games.
With Netherlands forward Memphis Depay likely out for the rest of the season as he recovers from a serious knee injury, Lyon is fighting to keep Dembélé. Chelsea is reportedly keen on signing