Atalanta led twice with Guglielmo Stendardo first to put them ahead in the eighth minute before Thereau levelled in the 76th.
Luigi Giorgi restored Atalanta's lead six minutes from time only for Thereau to level with almost the last kick of the game.
Chievo had the first chance of the game in the fifth minute when Thereau hesitated with the goal gaping to instead set up Adrian Stoian, whose lobbed effort went over the crossbar.
Atalanta responded and opened the scoring with their first attack of the game.
Luca Cigarini's free-kick from close to the corner flag was headed on by German Denis, providing Stendardo with an open goal to aim for and the central defender made no mistake in tucking home.
Just a minute later De Luca nearly made it two but Lorenzo Squizzi managed to make a save at the second attempt.
Squizzi was tested again by Carlos Carmona after 30 minutes, but he managed to turn the ball behind for a corner.
Marko Livaja, recalled to the Atalanta side after being left out for disciplinary reasons in recent weeks, nearly marked his return with a goal early in the second half when he burst into the penalty area, but Squizzi denied him.
Minutes later, Livaja did find the back of the net from Cigarini's cross, but the goal was ruled out for offside, even though the on-loan Inter Milan striker took a while to realise it and was shown a yellow card for removing his shirt in celebration.
But there was no doubt about Thereau's equaliser at the other end in the 76th minute.
Chievo's top goalscorer needed only one touch to convert Stoian's lofted ball with a diagonal shot from a tight angle into the far corner of Ciro Polito's goal.
At that point the game appeared to be heading for a draw, but Giorgi had other ideas.
He picked up a poor clearance on the edge of the penalty area and volleyed the ball beyond Squizzi and into the far corner with his favoured left foot in the 84th minute.
There was to be one final twist, though, as Thereau scored his 11th goal of the season as Atalanta failed to clear their lines from a corner, the Frenchman on hand to turn the ball in from close range.