The veteran defender added to Massimo Maccarone's penalty midway through the first half to lift Mario Beretta's team - who had started the day in the bottom three on goal difference - up to 15th in the table and leave them safe by a single point.

Tommaso Rocchi had threatened to give Siena reason to rue their one-point deduction at the start of the season for a late social security payment when he hit an equaliser from the spot 17 minutes from time.

While the win was met with jubilation at the Artemio Franchi, it was greeted with devastation in Verona, as Chievo's defeat away to Catania meant they took Siena's spot in the drop zone.

AC Milan's defeat to Reggina saw Lazio, whose place in next season's Champions League qualifying round was already confirmed, hold on to their third place.

After an understandably cagey opening, with the home side desperate not to make a mistake which could kill off any escape act before it had even got underway, Siena made the breakthrough on 23 minutes.

Maccarone tumbled in the area under a clumsy challenge from Guglielmo Stendardo and the former Middlesbrough striker got up and held his nerve to convert the resulting penalty.

The opening goal helped relieve some of the tension in the ground and Maccarone almost doubled the lead in the 39th minute, but his volley from the edge of the box flew just wide of a post.

Midfielder Ezio Brevi could have sent them into the break firmly in the driving seat, but he missed the target on the stroke of half-time.

Although Siena began the second period as they had finished the first against a Lazio side which did not appear too concerned about finding away back into the match, it was the team from Rome who came closest to scoring.

Enrico Chieso played in Simone Vergassola, whose shoot Siena goalkeeper Alex Manniger but was just off target.

That threat showed the fragility of Siena's lead and the strugglers were made to pay for not making the most of their dominance when Lazio pulled level in the 73rd minute.

Negro, who enjoyed 12 years with Lazio during which he was capped by the national side, brought down Tommaso Rocchi in the box and his former team-mate showed no mercy by converting from the spot.

Staring relegation in the face, Siena went for broke and on 80 minutes Daniele Galloppa should have done better when unmarked in front of goal.

And with his team just five minutes away from Serie B, Negro made amends for his earlier error with a close range finish to keep Siena up and break Chievo hearts.