Napoli welcomed on-form Lazio looking to bite into their seven-point deficit to leaders Juventus, compounded by their 2-1 defeat to the champions in Turin last week.

But despite thrilling fans with a dominant first-half display that saw Belgian international Dries Mertens notably miss a series of chances, Maurizio Sarri's men are in danger of trailing Juventus by nine points if the Turin giants beat Chievo in Verona on Sunday.

After Mertens and Lorenzo Insigne came close before the break, Hamsik eventually broke the deadlock with a well-taken strike from Faouzi Ghoulam's delivery, beating Federico Marchetti in the Lazio net seven minutes after the restart.

But the hosts' earlier misses returned to haunt them when Keita Balde levelled less than two minutes later.

A blunder by Marco Parolo in the area saw Senegal striker Keita pounce and control well on the right side of the box before beating Pepe Reina from close range.

Napoli should have added to their tally, but the ball stayed out.

On the hour Hamsik ran on to Mertens' flick in the area but was dispossessed at the last moment. 

From the resulting corner Insigne's header appeared to come off the arms of Parolo then Immobile but there was no call.

Insigne skewed wide before being replaced by Manolo Gabbiadini, who just failed to reach Mertens' long threaded ball down the middle and saw claims for a penalty waved away when he fell under a challenge inside the area.

Napoli remain in fifth, with Lazio a point ahead in fourth after claiming a valuable third draw in a seven-game unbeaten streak that stretches back to a 2-0 defeat to AC Milan on September 20.

Earlier, England goalkeeper Joe Hart narrowly avoided a goal-line howler as an Andrea Belotti brace inspired a rampant Torino to a 5-1 win over Cagliari that took their goals tally to a league-leading 27.

"It's our best game of the season so far. The lads were great, they played with a boxer's spirit," Torino coach Sinisa Mihajlovic told Sky Sport. 
"At the end of the first half we took our foot off the pedal, and conceded another headed goal.

"But we have the best attack in Serie A, and we're playing some nice football."

Hart was rarely troubled, although the Englishman fumbled a Gianni Munari shot that went over his head and, after bouncing behind him, came dangerously close to going over the line before he plucked it to safety.

Goal-line technology declared no goal and Torino went on to take a 3-1 lead into half-time.
Hart was then beaten fairly and squarely when Federico Melchiorri rose to send a powerful header past the 'keeper's hand and inside the near post.
But Daniele Baselli stretched the hosts' lead six minutes after the restart, and when Belotti won a penalty on the hour he stepped up to beat Storari for the second time.
Cagliari's Daniele Dessena was issued a straight red card for protesting the penalty call, having grabbed the referee's arm after he had raised it to caution Diego Farias for the foul.