Antonio Nocerino's early goal set Milan on their way and Zlatan Ibrahimovic sealed the win midway through the second half with a superb strike as the league leaders took full advantage of Juventus' slip-up.
Milan dominated throughout after Nocerino's seventh-minute strike put them ahead and the only surprise was that they only added one more goal to their tally against relegation-threatened Lecce.
Juventus had more than enough chances to beat Genoa but in the end had to settle for their fourth successive Serie A draw.
Simone Pepe had a goal ruled out for a debatable offside decision after also hitting the post, while Mirko Vucinic also struck the woodwork twice as Juve sought to get back to winning ways.
The visitors could find no way through and chalked up their 14th draw of the season.
Third-placed Lazio missed the chance to close the gap by falling 3-1 to in-form Bologna.
The Roman outfit could have pulled to within one point of Juve but had two men sent off.
Daniele Portanova put Bologna ahead in the 11th minute before Alessandro Diamanti doubled the advantage before the half-hour mark, and Francesco Matuzalem was shown a red card for catching Diamanti in the face before the interval.
An own goal from Matteo Rubin in the 56th minute reduced the arrears to one but the hosts had Alvaro Gonzalez sent off two minutes later.
Rene Krhin restored the visitors' two-goal lead 15 minutes into the second half and Bologna remained unbeaten on the road this year.
Fifth-placed Udinese also suffered a shock 1-0 defeat as Attilio Tesser made a winning return to the Novara bench.
Tesser was reappointed as Novara coach this week after Emiliano Mondonico was unable to turn around their fortunes, and the fans' favourite managed to inspire the Piedmontese side to their fourth win of the season.
Jeda scored the winning goal in the 16th minute as Novara picked up their first win in three months to move three points ahead of Cesena, now alone at the foot of the table.
However, Novara still face an uphill challenge to avoid relegation, with 11 points still separating them from safety.
Catania took a giant step towards survival with a narrow 1-0 victory over Fiorentina at the Angelo Massimino stadium.
Francesco Lodi struck the only goal of the game from the penalty spot in the 58th minute to hand the Sicilians their 10th victory this season.
The result has lifted Catania to eighth in the standings, just two points from the 40-point mark, a figure deemed sufficient to avoid relegation.
Atalanta missed a chance to climb into the top half after a 1-1 draw at home to Parma.
Thomas Manfredini spectacularly put Atalanta ahead in the fifth minute but Parma got a deserved equaliser through Gabriel Paletta before the hour mark to clinch a point and leave them six clear of the drop zone.
Luca Ceccarelli's dismissal proved the turning point as strugglers Cesena were defeated 2-0 by Siena at the Stadio Dino Manuzzi.
The defender was sent off in the 74th minute after bringing down Emanuele Calaio in the penalty area as he ran clear on goal.
The hosts had dominated up to that point but Franco Brienza followed up Claudio Terzi's missed spot-kick to score and then set up Erjon Bogdani to seal the victory.
Roma regained sixth spot from Inter Milan with a 1-0 win against Palermo at the Stadio Renzo Barbera.
Fabio Borini's goal in the third minute was enough to earn the Giallorossi all three points and inflict the second home defeat in a row on Palermo, whose coach Bortolo Mutti will be fearing a call from club president Maurizio Zamparini.
Napoli overcame the absence of star man Edinson Cavani to sweep aside Cagliari in a 6-3 thriller at Stadio San Paolo.
Cavani was rested by Napoli coach Walter Mazzarri ahead of next week's Champions League clash with Chelsea but the home side still possessed plenty of attacking threat.
Marek Hamsik, Paolo Cannavaro, Christian Maggio, Walter Gargano and Ezequiel Lavezzi shared Napoli's goals, with Cagliari defender Davide Astori contributing an own goal.
Joaquin Larrivey scored a hat-trick in reply for Cagliari to enjoy some personal glory, but it could not prevent a humbling defeat.
In Friday night's other game, Inter Milan left it late to beat Chievo with two goals in the last three minutes earning them a 2-0 win at Stadio Bentegodi.
Chievo had frustrated Inter throughout, but just when it looked like they had done enough to earn a point, Walter Samuel headed Inter in front.
Diego Milito, who missed a penalty in the 14th minute, sealed the win in stoppage time to lift some of the pressure from Inter coach Claudio Ranieri.