Inter Milan's eight-match winning run in Serie A came to an end as two of their former players, Antonio Candreva and Keita Balde, struck to give Sampdoria a shock 2-1 win in Genoa on Wednesday.
Candreva converted from the penalty spot before Keita guided home a finish to give the hosts a two-goal lead at the interval, and a Stefan de Vrij header was all Inter could muster in response.
Alexis Sanchez had a penalty saved by Emil Audero early on but Inter struggled to threaten in the absence of striker Romelu Lukaku, who was only fit enough to feature for the final half hour and couldn't inspire a comeback.
It meant Antonio Conte's side squandered the chance to go top of the table ahead of AC Milan, who play Juventus later on Wednesday.
Inter remain in second place on 36 points, one behind their city rivals, while Sampdoria are 11th on 20 points.