(CNN) -- While city rivals Inter were winning the Club World Cup in Abu Dhabi, Serie A leaders AC Milan crashed to a 1-0 home defeat to AS Roma on Saturday night.
It was their first defeat in eight matches as a goal from Marco Borriello, who is on loan from Milan, in the 69th minute gave Claudio Ranieri's men the three points.
The Rossoneri had surged six points clear at the top last weekend but Juventus, Lazio and Napoli could all cut the gap back to three points if they win their matches on Sunday.
Defending champions Inter trail the leaders by 13 points, but have two games in hand, while Roma revived their chances ahead of the three-week winter break by moving into fifth, but still seven points adrift.
Milan had much of the play in the San Siro and Zlatan Ibrahimovic should have scored when put clean through by Gennaro Gattuso's fine pass but shot weakly at Doni in the visiting goal.
Borriello's goal from close range stunned the leaders but Ibrahimovic wasted a chance from a similar position as in the first half while subsitute Ronaldinho went close with a spectacular bicycle kick.
It was Roma's fourth win in five games against Milan.
In the other Serie A match played on Saturday, Cesena ended 2010 with a much-needed 1-0 win over Cagliari which ensures they will not end the year rock-bottom in Serie A.
A goal from Luis Jimenez in the 17th minute was enough to settle the match on a frozen surface at the Stadio Dino Manuzzi.