Seventh-placed Juve had been making a push for a European spot despite a 15-point deduction for false accounting, winning seven of their previous eight league matches before losing to Lazio last weekend.
Sassuolo broke the deadlock on 64 minutes when Nicolo Fagioli tried to clear a corner but Defrel did well to control the ball and place it into the bottom right corner.
Juve are now four points behind Atalanta who occupy the last European place, however the side from Lombardy have a game in hand.
The Bianconeri host league-leaders Napoli next.
AAP
