Former Manchester United forward Paul Pogba struck in injury time to hand Juventus a 2-1 win over Bologna on Wednesday as the champions opened up a six-point gap on Napoli.
Juventus looked set for a share of the points until Pogba got his head to a superb cross from the left from Sebastian Giovinco to beat Federico Agliardi from close range in the dying seconds.
The Turin-based giants' ninth win in 10 games extended their unbeaten run to 49 games and stretched their lead over Napoli to six points after Walter Mazzarri's side suffered a shock 1-0 defeat away to Atalanta.
Elsewhere, Inter Milan kept in touch with the leaders with a come-from-behind 3-2 win over Sampdoria while Roma suffered a shock 3-2 defeat away to Parma and Lazio had to settle for a draw at home to Torino.
Cagliari celebrated their biggest win of the season when they beat Siena 4-2 to consolidate their mid-table position, while second-from-bottom Chievo grabbed only their third win of the season with a 2-0 defeat of Pescara.
In another mid-table battle Udinese drew 2-2 with Catania.
AC Milan battled to a 2-2 draw away to Palermo on Tuesday.
Juventus lead second-placed Inter by four points while Napoli dropped to third place on 22. Lazio are fourth on 19 while Fiorentina, who travel to Genoa on Thursday, are fifth on 15.