Inter Milan's hopes of challenging for the Serie A title got off on the wrong foot with a shock 1-0 defeat at Sassuolo on Sunday.
New-look Inter boasted four new signings in their line-up plus Croatia World Cup finalist Marcelo Brozovic.
But Domenico Berardi's 27th-minute penalty, after Joao Mario brought down Federico Di Francesco, gave Sassuolo their win over a disappointing Inter, who have lost seven of their past 11 matches against the Neroverdi.
Inter gave debuts to Lautaro Martinez, Stefan de Vrij, Matteo Politano and Kwadwo Asamoah at the start while Keita Balde came on during the second half, but their biggest signing, midfielder Radja Nainggolan, missed the game with a muscular injury.
The scoreline could have been worse as Kevin-Prince Boateng hit the post on his Sassuolo debut.
Sassuolo goalkeeper Andrea Consigli denied Inter a late equaliser with a superb point-blank save from De Vrij's header, but otherwise was given little to do by a toothless Inter attack.