Title-challengers Napoli closed the gap to Serie A leaders Juventus to nine points thanks to a 2-0 win over outclassed Genoa at the San Paulo on Sunday.
Inter, meanwhile, saw their hopes of a place in next season's Champions League kept in check by a shock 4-3 reverse to Atalanta, for whom Argentine German Denis scored a hat-trick.
Inter's 11th reverse of the season ended amid ugly scenes as Ezequiel Schelotto remonstrated with several of his former Atalanta teammates and had to be held back by security.
The visitors' coach Stefano Colantuono told Sky Sport there was little surprise in the result: "We prepared for this game really well and I can only praise the efforts of the whole team."
Juve, who were given a scare by strugglers Pescara on their way to a 2-1 win on Saturday, are still top with a nine-point lead on Napoli with Milan still third but four points off second place after giving up a two-goal lead in a 2-2 draw away to Fiorentina.
Fiorentina, in fourth, are six points further off the pace but two ahead of Lazio ahead of the 'Derby della Capitale' on Monday away to Roma, with Inter sixth also on 50 points.
Genoa gave Napoli a scare after just two minutes when Andrea Bertolacci unleashed a shot which Morgan De Sanctis did well to parry.
However that was just about all the visitors had to offer in the opening half as Naploli took control on their way to a 2-0 half-time lead.
Genoa keeper Sebastien Frey, who later saved a penalty from Edinson Cavani, did well to parry from Goran Pandev's drive and the forward threatened again 10 minutes later when he cut inside to unleash a shot that went inches past the upright.
Pandev made no mistake minutes later with Cavani's pass after the Uruguayan had won the ball back just out side the area, controlling well as Genoa's defence retreated to fire home in off the underside of the crossbar.
Cavani turned provider again on the half hour, this time feeding Marek Hamsik in midfield before the Slovakian found Blerim Dzemaili unmarked to the left of goal and free to send a low strike under Frey.
Napoli resumed in similar fashion after the break, but opportunities from Cavani, Hamsik and Pandev all failed to hit the net as Genoa reinforced at the back.
"We're not looking at other teams," said Napoli coach Walter Mazzarri.
"We're just focusing on what we have to do, we're going through a good period and I'm happy we didn't concede any goals."
At the San Siro striker Tommaso Rocchi made the most of a rare start for Inter by putting the hosts ahead in the 43rd minute.
But in a second half that was just as lively for the off-the-ball action, it was a case of tit-for-tat as both sides went on a 20-minute, six-goal scoring spree.
Giacomo Bonventura levelled for Atalanta on 56 minutes, only for Gabriel Alvarez to restore the Nerazzurri's lead a minute later.
Four minutes later Alvarez struck again to give Inter a two-point cushion, only for Denis to level from the penalty spot on 65 minutes.
Denis grabbed his second six minutes later and completed his hat-trick in the 77th minute to give the Bergamese side a shock 4-3 lead.
Inter should have levelled at the death however defender Andrea Ranocchia somehow skewed the ball high and wide only two metres out with the goal at his mercy.