France forward Valbuena scored each side of the interval as Marseille, who won the last two editions of the competition, strolled past Caen with another goal by Loic Remy.
Valbuena, who has scored in his last four games, put the visitors ahead after seven minutes with a curled free-kick and it quickly looked like there would barely be a contest at the Michel d'Ornano stadium.
Marseille were without the influential Ayew brothers up front, after the Ghana forwards left to join the Black Stars ahead of the January 21-February 12 Africa Cup of Nations, but Valbuena and Remy more than compensated for their absence.
Remy made it two from close range in the 19th minute after Morgan Amalfinato had connected with a brilliant long-range cross from Benoit Cheyrou to set up the France striker.
Valbuena was at the receiving end of another fine cross from Cheyrou after Lucho Gonzalez let the ball pass between his legs to volley home and put the result beyond doubt seven minutes into the second half.
On Wednesday, Olympique Lyon will take on French champions Lille while Nice play Dijon and Le Mans, the only non Ligue 1 side left in the competition, host Lorient.
