Serie A leaders Inter Milan suffered a stunning 3-1 defeat at Atalanta on Sunday to blow the title race wide open. Second-placed Juventus can cut Inter's advantage at the top to a point if they win at Lazio in the late game.
Striker Sergio Floccari grabbed a superb opener for mid-table Atalanta on 18 minutes and playmaker Cristiano Doni soon extended their lead with a deflected free kick and a powerful header in the first half.
Jose Mourinho used all his three substitutes by the start of the second half but his side barely mustered a shot on target before Zlatan Ibrahimovic netted a consolation in injury time.
"I can't explain it," Mourinho told Sky television before he clashed with interviewers. "I should keep quiet and let the sports press use any adjective they want, which I must accept given my team played such an awful match."
The champions had won eight league matches in a row before drawing 1-1 at home to Cagliari last weekend and letting Juve move within four points.
Bergamo-based Atalanta have always been a threat at home and this season 22 out of their 27 points have been won in their own stadium.
Genoa climbed up to fourth, the final Champions League qualifying spot, thanks to a 2-0 win at Lecce and fifth-placed Napoli's controversial 2-1 defeat at joint-bottom Chievo.
Chievo moved level on points with Reggina, who lost 1-0 at Siena on Saturday, following two Michele Marcolini penalties although replays suggested Simone Bentivoglio dived to win the second spotkick.
Last season's runners-up AS Roma, who had a terrible start to the campaign, are now just five points off a Champions League place after a wonderful overhead kick from Julio Baptista in injury time sealed a 1-0 win at lowly Torino.
AC Milan in third are six points behind Inter after a 1-0 home win over Fiorentina on Saturday in what could be Kaka's last game for the club if he and Milan accept a huge bid from Manchester City.
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