Raúl Albiol secured three points for Carlo Ancelotti's side to keep the pressure on the leaders while Krzysztof Piatek struck again for Genoa.
Napoli beat lowly SPAL 1-0 on Saturday to move within five points of Serie A frontrunners Juventus.
Defender Raúl Albiol nodded home a corner kick in added time before the break for the winner.
Napoli provided little danger throughout although Dries Mertens hit the post in the second half. Alex Meret also had to make two late saves to preserve the three points after two late efforts from the visitors.
Napoli have 41 points, with Juve on 46 ahead of their Saturday night date with Roma.
Genoa's Krzysztof Piatek struck late in a 3-1 defeat of 10-man Atalanta to take his tally to 13 goals for the season and edge ahead of Cristiano Ronaldo.
Piatek was involved when Atalanta's Rafael Toloi deflected into his own goal and he then fired into the top right corner on 88 minutes. Duvan Zapata levelled for 1-1 with a penalty and Darko Lazovic scored Genoa's second.
Rafael Toloi was sent off in injury time AC Milan were stunned 1-0 at home by Fiorentina and slipped to fifth behind Lazio as young inernational Federico Chiesa fired home the winner on 73 minutes.
Lazio beat Cagliari 3-1 to go fourth in the race for a Champions League place.
A drive from Sergej Milinkovic-Savic and Francesco Acerbi's tap-in rewarded a furious first half hour from the hosts. Senad Lulic struck after the break before the Sardinians pulled one back from a late penalty awarded after video review and converted by João Pedro.
The Romans are now one point ahead of Milan. Cagliari are 13th with a five-point cushion to the drop zone.
Sampdoria are sixth, one point behind Milan, after a 4-2 win at Empoli thaks to a late brace from substitute Gianluca Caprari.
Sassuolo and Torino drew 1-1 and Udinese also drew 1-1 with Frosinone, who had new coach Marco Baroni at the helm.