Inter closed the gap at the top of Serie A as Romelu Lukaku's penalty sealed a dour 1-0 victory over 10-man Napoli at San Siro on Wednesday.

With local rivals Milan held to a 2-2 draw at Genoa, the Nerazzurri reduced the league leaders' advantage in the standings to one point thanks to Lukaku's 73rd-minute spot-kick.

A rash challenge from David Ospina enabled the Belgium striker to wrap up a fifth straight league win for Inter, and with Lorenzo Insigne seeing red for dissent there appeared to be no way back for Napoli.

Inter struggled to close the game out, though, with Samir Handanovic making two important saves before the post stopped Andrea Petagna earning a share of the spoils for Napoli.

Napoli were dealt an early blow when Dries Mertens appeared to tweak his ankle while digging out a cross before the ball ran out of play and had to be replaced by Petagna in the 16th minute.

Lautaro Martinez almost added to their woes within 30 seconds but his shot on the spin skidded wide after Kalidou Koulibaly's wayward pass enabled Nicolo Barella to feed the striker.

Napoli enjoyed the lion's share of possession but chances were few and far between, with Piotr Zielinski volleying wide and Roberto Gagliardini producing the only effort on target before the break with a tame header.

Hirving Lozano volleyed over after controlling a brilliant pass from Insigne, who forced Handanovic to make his first save of the game with an improvised flick in the 69th minute.

The game turned in Inter's favour when Ospina was deemed to have fouled Matteo Darmian in the box and Insigne's protests resulted in him being sent off.

Lukaku tucked the penalty into the bottom-left corner but Inter needed Handanovic and a slice of luck to ensure they did not throw the win away late on.

Handanovic kept out Matteo Politano – on loan at Napoli from Inter – and Giovanni Di Lorenzo before Petagna found the base of the upright in the 92nd minute.