Arkadiusz Milik scored a first-half hat-trick as Napoli eased into the last-16 of the Champions League with a 4-0 home win over Genk.

With the Belgian side already consigned to finishing bottom in Group E, all the pressure was on Carlo Ancelotti's men at Stadio San Paolo on Tuesday.

Yet any concerns for the hosts disappeared once Milik opened the scoring after just 125 seconds, capitalising on an error by teenage goalkeeper Maarten Vandevoordt, before adding two more before the break.

Dries Mertens netted Napoli's fourth from the penalty spot but Liverpool's win away in Salzburg means the Serie A side finish second in the group, behind last season's winners.

Vandevoordt became the youngest goalkeeper to start a Champions League game but the 17-year-old made a massive mistake to hand Napoli, who had already hit the bar through a Kalidou Koulibaly header, a third-minute lead.

Given an early touch of the ball by his defence, Vandevoordt tried to turn into space away from Mertens but succeeded only in presenting Milik with a tap-in.

The forward scored again in the 26th minute, converting a low right-wing cross from Giovanni Di Lorenzo, before completing his treble from the spot.

Vandevoordt was at fault again, bringing down Jose Callejon, and the teenager was sent the wrong way from 12 yards.

A one-sided opening 45 minutes allowed Napoli to ease off after the break, but they struck again from the spot when Casper De Norre was harshly penalised for handball.

Mertens stepped up to beat Vandevoordt with a Panenka, completing the youngster's humiliation.

What does it mean? Questions over Ancelotti continue despite progression

Napoli missed out on the knockout rounds a year ago despite having been in a strong position, but moving into the last 16 is no guarantee Ancelotti will be in charge for their next game in the competition.

Rumours he is set to be replaced by ex-AC Milan boss Gennaro Gattuso continue to build in Italy.

Milik maintains hot streak

Poland international Milik made the most of a clear gulf in class with a first-half treble, becoming the first player for a Serie A side to achieve that feat in the Champions League since March 2000. He has now hit nine goals in his past seven appearances for club and country.

Worst possible start for Vandevoordt 

With Genk already guaranteed to finish bottom of the group, Vandevoordt was given a chance to impress by coach Hannes Wolf. The teenager will hope to forget his Champions League debut, given his horrible early lapse.

What's next?

Parma are the visitors to Naples in Serie A on Saturday. Genk, meanwhile, host Waasland-Beveren in the Belgian top-flight on the same day.