The inconsistent Italy international, who has argued his recent sluggish performances have been down to tendonitis, scored twice and set up the other goal as the Serie A leaders put the pressure on their title rivals.

Saturday's victory not only gave a huge boost to Del Piero's confidence, but also enabled Juve to open up a six-point lead over second-placed AC Milan, who host city rivals Inter Milan on Sunday.

Del Piero, whose was a major disappointment for Italy at Euro 2004, insisted he is slowly starting to find his feet after a difficult start to the season.

"My physical condition is improving all the time and I think its starting to show," said the 29-year-old forward.

"However I'm not getting too excited and I have to complete my rehabilitation, even if I feel that I am on the right road."

Juventus coach Fabio Capello admitted Del Piero was not yet firing on all cylinders, but was encouraged by what he saw in Tuscany.

"He needs time to get back to being 100 per cent, but today he did things that we haven't seen for a while," he said.

"His goals are important for his confidence and the morale of the team."

Capello was relieved to see his team survive the first half which was dominated by the home side, but ended goalless.

"We played well against difficult opponents, who caused us quite a few problems and could have scored several times," he added.

"But this squad has great personality and conviction and in the end we came out on top."

Del Piero broke the deadlock in the 52nd minute, prodding home from close range after Zlatan Ibrahimovic's header had struck the legs of Siena keeper Marco Fortin.

He doubled his tally on the hour, chesting down Jonathan Zebina's cross before rifling a low drive through Fortin's legs.

Del Piero then turned provider, his crossed free-kick headed home by Argentina-born wingback Mauro Camoranesi.

Earlier Saturday, Cagliari escaped with a 2-2 draw away to struggling Atalanta despite playing the last 40 minutes with 10 men.

The visitors had Massimo Brambilla sent off for a second yellow card shortly after half time, but the Sardinians survived a second half onslaught to earn a share of the spoils in Lombardy.

A point for Cagliari saw them draw level with Inter Milan on 10 points, while Atalanta remain third from bottom and are still looking for their first win.

Giampaolo Pazzini gave Atalanta a second minute lead with a neat chip before Gianfranco Zola's superb diagonal pass set up Mauro Esposito for an easy equaliser.

Cagliari then went ahead in the 29th minute. Zola's free-kick to the back post was headed across the face of goal by Massimo Gobbi to give Simone Loria a simple tap-in.

Atalanta levelled the score five minutes from half time when Demetrio Albertini's shot was deflected into the path of Riccardo Montolivo, whose low drive found the bottom corner.