After a two-year spell in the second tier of French football, Caen returned to top-flight action on Saturday and made an excellent start to the new campaign.
Ngolo Kante gave them the lead after 12 minutes at the Parc des Sports and Duhamel netted twice in five minutes prior to the interval.
No further goals came the way of Patrice Garande's side, but the damage had already been done and Caen moved top of the table.
Saint-Etienne also enjoyed a winning start on their travels as Turkish striker Mevlut Erdinc struck both goals in a 2-0 victory at Guingamp.
Marseille thought they were on course for three points in Marcelo Bielsa's first competitive match in charge after taking a 3-1 lead against Bastia.
However, Gadji Tallo and Christopher Maboulou scored to rescue a 3-3 draw and ensure another new boss, Bastia's Claude Makelele, was able to celebrate a point.
Maboulou had given Bastia an early lead, only for Andre-Pierre Gignac to score twice either side of a Christian Romaric own goal.
Nice were another side to come from behind on Saturday as a Dario Cvitanich double and Alexy Bosettii's 68th-minute winner saw them beat Toulouse 3-2.
Cheick Diabate grabbed the only goal of the game at the Stade de la Mosson as Bordeaux defeated Montpellier 1-0, while newly promoted Lens were sunk by the same scoreline at Nantes.
With their participation in Ligue 1 only confirmed on July 28 after complications with their financial security, Lens will have been pleased to simply be playing at the Stade de la Beaujoire, but they were denied a point by Yacine Bammou's second-half strike.
Meanwhile, Ligue 2 champions Metz got off to a solid start with a goalless draw against UEFA Champions League participants Lille.
