Dembele scored France's third goal, curling a fine finish past goalkeeper Salvatore Sirigu from the edge of the penalty area, having earlier hit the crossbar at the end of an impressive run.
Mbappe is widely regarded as one of the world's finest youngsters but the teenager thinks Dembele is the most promising in the game.
"It's a promising partnership. We get on well, we appreciate each other," the Paris Saint-Germain forward said following the win.
"I've always wanted to play with great players. I have two top players [next to me]: Antoine, top 10; Ousmane, the best young player in the world, for me.
"We all try to help each other."
7 - France have scored two goals or more in each of their last seven games, their longest run since 2000 under Roger Lemerre (12). Prolific. pic.twitter.com/AaR7QPANXU— OptaJean (@OptaJean) June 2, 2018
The 21-year-old suffered a hamstring injury in September that kept him sidelined until January, after which he struggled to hold down a regular place in Ernesto Valverde's first team.
With Barca linked with a €100m (£87m/$116m) bid for Griezmann, there have been suggestions they could allow Dembele to leave on loan, with Premier League pair Arsenal and Liverpool both said to be interested.