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Icardi, who was this week stripped of the captaincy amid ongoing speculation over his future, watched from the San Siro stands due to the knee injury that kept him out of the 1-0 Europa League victory over Rapid Vienna on Friday (AEDT).

Inter looked set to rue his absence until Danilo D'Ambrosio opened the scoring in the 73rd minute, but substitute Manolo Gabbiadini pounced on some shoddy defending just 25 seconds after coming on to pull Sampdoria level.

However, Nainggolan's shot from the edge of the box found a path through a host of bodies three minutes later to restore the Nerazzurri's four-point cushion over fourth-place AC Milan.

Lautaro Martinez, who scored Inter's goals in back-to-back wins over Parma and Rapid, led the line in Icardi's absence and was kept off the scoresheet by Emil Audero in the sixth minute.

Audero had to scramble back to stop a tame Ivan Perisic shot that squirmed through his legs crossing the line, while Milan Skriniar saw a goal ruled out for offside against D'Ambrosio in first-half stoppage time.

Samir Handanovic stayed on his feet to deny Gregoire Defrel just 32 seconds after the restart and the newly appointed captain produced a fingertip save to keep Fabio Quagliarella's looping header out in the 66th minute.

Perisic was unperturbed by seeing a shot saved by Audero and his run into the box from the left enabled D'Ambrosio to dart in front of Nicola Murru for the opener.

Gabbiadini punished Skriniar's failure to clear the ball with his first involvement after replacing Riccardo Saponara in the 75th minute, but Sampdoria was unable to hold on for a point.

Nainggolan somehow found the bottom-left corner with Audero unsighted to seal an important win that enabled Inter to strengthen its grip on third.