كتب : Amro Hassan
The win closes the gap between Juventus and Serie A leaders Inter to four points, after the Nerazzuri were held at home by Cagliari to a 1-1 draw on Saturday.
Influential skipper Alessandro Del Piero scored the only goal of the game on 33 minutes to hand the Old Lady the narrow win.
The defeat demotes Siena to 15th spot with 19 points.
In another game, Napoli beat Catania 1-0 to go fourth in the table with 33 points, while Catania stay ninth on 25 points.
While Lazio beat Reggina 3-2, Fiorentina were stunned at home by Lecce, who beat the Florence club 2-1.