Rafael Leao drove home the fastest goal in Serie A history to set leaders Milan on their way to a 2-1 win at Sassuolo. 

Milan head coach Stefano Pioli said on Saturday that Leao's recent performances had been "not up to standard", but there was no faulting his sharp finish after six seconds at the Citta del Tricolore stadium. 

The 21-year-old former Lille forward took a pass from Hakan Calhanoglu in his stride and, with his third touch, smashed the ball past home goalkeeper Andrea Consigli. 

Alexis Saelemaekers added a second in the 26th minute and Milan's lead rarely came under threat from sixth-placed Sassuolo until Domenico Berardi netted an 89th-minute free-kick that made for a briefly tense finish.

Pioli fielded a team with an average age of just 22 years and 313 days, Milan's second youngest line-up since the 2004-05 season, when Opta began collecting such data. 

There was no Zlatan Ibrahimovic, the team's 39-year-old leading scorer absent after suffering a calf strain in training as he prepared for a first-team return. 

But after Juventus showed they remain a part of the Scudetto conversation with an impressive 4-0 win at Parma on Saturday, it was Milan's turn to show their hand, and they had an ace up their sleeve. 

Leao put an emphatic finishing touch to Milan's immediate charge through the Sassuolo ranks, with Brahim Diaz playing the kick-off short to Calhanoglu, who raced straight towards the penalty area in what looked a well-rehearsed ploy. Calhanoglu's pass through to Leao was smashed in, leaving the home side shell-shocked and still yet to touch the ball. 

Milan thought they had a second goal in the ninth minute when Calhanoglu drove home low into the left corner from the edge of the penalty area, but a marginal offside in the build-up saw the goal disallowed after a VAR check. 

They were nevertheless in control and full value for their second goal when it arrived in the 26th minute. Theo Hernandez ran from deep inside his half down the left flank before darting infield and clipping a short pass that gave Saelemaekers a tap-in. 

Gianluigi Donnarumma made a fine diving stop to keep out a fizzing 25-yard shot from Mehdi Bourabia in the second half, before Milan threatened a third when Jens Petter Hauge's curling shot from similar range was pushed away by Consigli. 

Sassuolo had the final say as Berardi got his shot beyond the Milan wall, but the visitors survived.

 Ilicic lifts Atalanta

At the San Siro, Inter Milan extended their winning league run to six matches with Achraf Hakimi getting the first goal five minutes after the break.

Romelu Lukaku slotted in a penalty after 71 minutes for his 11th league goal this season after a M'Bala Nzola handball.

"This is our sixth straight Serie A win, we welcome these results because consistency will keep us competing at the top," said Conte.

"We didn't create a huge amount but we conceded almost nothing, it was a deserved win."

Roberto Piccoli got a goal back for Spezia, who are just above the relegation zone after extending their winless run to six games, deep into injury time.

Atalanta came-from-behind to crush Roma 4-1 in Bergamo despite playing without captain Papu Gomez who has fallen out with coach Gian Piero Gasperini.

Edin Dzeko scored after just three minutes with the Roma captain finishing off a Henrikh Mkhitaryan cross.

But Josip Ilicic came off the bench after the break to inspire the Atalanta recovery setting up Duvan Zapata for the equaliser just before the hour mark and the cross for Robin Gosens to head in ten minutes later.

Colombian Luis Muriel scored the third a minute after coming off the bench after 72 minutes before Ilicic got his first league goal of the season with an impressive solo run five minutes from time.

Atalanta, with a game in hand, are seventh in the table 10 points off leaders AC Milan.