Monfils beat top seed Rafael Nadal in his semi-final, while Tsonga received a bye when Roger Federer withdrew with a back injury, giving the bulky Frenchman an extra day’s rest.
That advantage ultimately told in the final, but Tsonga started sluggishly before rallying from 5-3 down in the first set as he claimed nine of the next 11 games against a fading opponent.
“At the beginning of the match Gael was incredible, he was everywhere,” Tsonga said in a court-side interview.
“I made him move a lot. Then he was a bit tired and I entered the court and my movement was really good.”
Tsonga and Monfils, each seeking their first titles since October when they won in Vienna and Stockholm respectively, began the match as fog billowed past the stadium floodlights and moisture settled on court.
Play was suspended early on for 35 minutes with the players complaining about the wet court.
When the match resumed, both men seemed tentative and hugged the baseline, with no respite from the mist.
At 6-5 down, Monfils crumbled, losing his serve to love to concede the set. Tsonga showed no let up, serving to love in the second set opener for his fifth straight game, a sequence that included winning 15 out of 16 points.
Monfils made it 1-1, but his anger simmered, shouting in frustration at one error, lobbing his racket after another,
Monfils pummeled a forehand wide to gift Tsonga the decisive break for a 4-2 lead and he saw out the match, earning two championship points with a nimble half-volley winner from mid-court.
(For more sports news and updates, follow Ahram Online sports on Twitter: @AO_Sports)