AC Milan overtook Lazio for the Serie A lead with a 3-1 win over Palermo on Wednesday, but lost Alexandre Pato and Filippo Inzaghi to injury with the derby against Inter Milan coming up next.
It's the first time Milan has had the sole lead since November 2008.
"We're going into the derby with a healthy dose of self-esteem," Milan coach Massimiliano Allegri said, looking ahead to Sunday's match.
Pato put Milan ahead in the 19th minute at the San Siro, Zlatan Ibrahimovic restored the lead with a penalty in the 77th and Robinho came off the bench to add the third goal in the 83rd.
Pato exited grasping his right thigh in the 65th and was replaced by Inzaghi, who appeared to twist his left knee in the 80th.
Lazio allowed a goal from Marco Parolo in the 85th minute and lost 1-0 at Cesena, its second consecutive defeat.
Milan has 23 points, Lazio is next with 22, Napoli has 21, while five-time defending champion Inter dropped to fourth with 20 after a 1-1 draw at Lecce, which equalized through Ruben Olivera in the 79th after Diego Milito had put the Inter in front eight minutes earlier.
Napoli won 1-0 at Cagliari while Juventus drew 1-1 at Brescia. Roma moved into sixth following a 3-2 win over Fiorentina.
Genoa beat Bologna 1-0 and Catania defeated Udinese 1-0.