Internazionale continued their relentless march towards the Serie A title with a 2-1 win in the Milan derby.
Ronaldo fired Milan into the lead five minutes before half-time but Julio Cruz levelled after 54 minutes.
Zlatan Ibrahimovic then clinched victory for Inter 15 minutes from time to keep them 16 points clear of their nearest challengers.
Second placed Roma had far too much for Udinese as they cruised to a 3-1 victory in the capital, with Francesco Totti excelling.
The club's talisman opened the scoring from the penalty spot in the 33rd minute before Simone Perrotta doubled their advantage in the 39th minute.
On the hour mark Totti grabbed his side's second, rendering Gyan Asamoah's strike mere consolation.
Palermo fell behind at home to Fiorentina as Adrian Mutu struck in the 32nd minute.
But Edinson Cavani's equaliser (70) left the final score at 1-1 and kept Palermo in contention for a European spot.
Palermo's dropped points allowed Lazio to move up to third though with a 3-2 victory at Reggina.
Giacomo Tedesco broke the deadlock for Reggina (25) but goals from Christian Manfredi (44) and Goran Pandev (45) gave Lazio a half-time lead.
Pasquale Foggia responded for Reggina (65), only for Ayodele Makinwa to pop up with a late winner for Lazio in the 80th minute.
High-flying Empoli were held to a 2-2 draw by Livorno despite going 2-0 up through Francesco Pratali (28) and Sergio Almiron (49).
Rahman Rezaei gave Livorno hope after 58 minutes and Cristiano Lucarelli salvaged a draw in stoppage time.
Struggling Parma grabbed a crucial late point as they drew 1-1 at Atalanta, but they fell to the bottom of the table as Ascoli beat Siena.
Mario Defendi struck for Atalanta after 53 minutes, before Ferdinand Coly drew Parma level with two minutes remaining.
A Sasa Bjelanovic strike after 22 minutes gave Ascoli a 1-0 win at Siena.
Chievo and Messina also played out a 1-1 draw, with Paolo Sammarca scoring a penalty for Chievo (73) and Cristian Rigano (86) netting for Messina.
Alessandro Rosina was on target as Torino defeated Catania 1-0.
Click below for individual match summaries:
Atalanta 1-1 Parma
Chievo 1-1 Messina
Empoli 2-2 Livorno
Internazionale 2-1 Milan
Palermo 1-1 Fiorentina
Reggina 2-3 Lazio
Roma 3-1 Udinese
Siena 0-1 Ascoli
Torino 1-0 Catania