French defender Heurtaux slotted home from close range to give the visitors the lead for the second time in the game after Nicolas Lopez's early effort had been cancelled out by Luca Siligardi.
They held on to move seven points clear of their 18th-placed opponents, who are guaranteed to spend the festive period in the bottom three of Serie A.
In the other game, Napoli dropped points in their bid to close the gap on second-placed Roma as they were held to a 1-1 draw at Cagliari.
Nene opened the scoring for Cagliari at the Stadio San Elia in the ninth minute but the opening goal was cancelled out from the penalty spot by Gonzalo Higuain 10 minutes later.
Napoli go in to the winter break two points behind Roma having played an extra game.