Danilo D'Ambrosio fired the hosts ahead from close range after 73 minutes at the San Siro.

Manolo Gabbiadini equalised, but Nainggolan's low shot - the third goal in the space of five minutes - sent Sampdoria to a third straight defeat.

Victory took Inter four points ahead of city rivals AC Milan in fourth, while Sampdora remain 10th.

Luciano Spalletti's side were without the injured Mauro Icardi, who has been stripped of the club captaincy amid protracted talks over a new contract.

Elsewhere, second-placed Napoli were held to a goalless draw at home to Torino.

Lorenzo Insigne missed the hosts' best chance, firing a powerful effort against the crossbar from the edge of the area.

The stalemate leaves Carlo Ancelotti's team 13 points behind leaders Juventus, who face Atletico Madrid on Wednesday in the first leg of their Champions League last-16 tie.