Napoli consolidated their position at the top of Group B as goals from Marek Hamsik, Arkadiusz Milik and a Dries Mertens double secured an impressive 4-2 victory over Benfica at Stadio San Paolo.

Maurizio Sarri's side were allowed to run riot at the start of the second half, scoring three goals in the space of just seven minutes to turn what had been a closely-fought contest into something of a rout.

Hamsik gave the hosts the lead on 20 minutes when he nodded home a Faouzi Ghoulam corner before Mertens curled home a sublime free-kick early in the second half.

Milik then added the third from the penalty spot and Mertens bagged his second from close range, with Gonacalo Guedes and substitute Eduardo Salvio netting nothing more than a consolations for the visitors.

The victory extends Napoli's unbeaten run to 11 games in all competitions, while for Benfica, it was a first defeat of the season.

The result also maintains Napoli's 100 per cent start to their Champions League campaign, while Rui Vitoria's men are still searching for their first win having been held at home by Besiktas on matchday one.

The tone for an entertaining first half was set in the opening minute when Milik latched on to a fine long ball from Ghoulam but Julio Cesar comfortably gathered the Pole's toe-poke finish.

Benfica responded almost immediately as Kostas Mitroglou just failed to scramble home the loose ball after Pepe Reina could only palm away a Nelsinho cross.

And the Greece international then saw his 15-yard strike parried by the Napoli goalkeeper after excellent approach work down the left from Alejandro Grimaldo.

But it was the home side who took the lead on 20 minutes as Hamsik took advantage of the visitors' failure to position a man on the near post by meeting Ghoulam's pinpoint corner and glancing a header past Cesar.

Milik came close to doubling his side's advantage just short of the half-hour, narrowly failing to slide home a low free-kick whipped into the box by Jorginho. 

Napoli were not to be denied at the start of the second half, however, as Mertens made it 2-0 by bending home a superb free-kick after being fouled on the edge of the box by Lisandro Lopez.

Jose Callejon was then clumsily upended in the box by Julio Cesar, allowing Milik to fire home his seventh goal in eight games from the spot.

And Mertens claimed his second from close range when Julio Cesar failed to deal with a cross, Milik deflected the ball back across goal and the Belgian nudged it home.

Substitute Guedes then took advantage of some sloppy home defending to pull one back for the visitors.

With the points in the bag, the Italian side switched off again four minutes from time, allowing Andre Almeida to pick out Salvio who chested the ball down and calmly fired past Reina, but the damage had already been done.