Marco Materazzi scored twice, once from the penalty spot, as Inter Milan won 2-1 at Siena on Sunday to clinch their second successive Serie A title with five games to spare.

The win, coupled with second-placed AS Roma's 2-1 defeat at Atalanta gave Inter an unassailable 16-point lead. Inter have 84 points from 33 games, Roma have 68.

"The emotion is immense," Inter coach Roberto Mancini told SKY. "The team have had an extraordinary championship. It is extraordinary to win five games from the end with a lead of 16 points.

"The team showed great character. I'm happy for all Inter fans."

After the match, Inter chairman Massimo Moratti announced that he had renewed Mancini's contract until 2011, with an option for a further extension to 2012.

Materazzi put Inter ahead in the 18th minute with a right-footed shot following a goalmouth scramble only for defender Paolo Negro to head in Siena's equaliser three minutes later.

Inter regained the lead 15 minutes after the break, when Siena keeper Alexander Manninger brought down Julio Cruz in the area and Materazzi converted the penalty.

Siena fought back and had several good chances to level but Inter hung on despite effectively playing the closing stages with 10 men, because Brazilian defender Maicon was carrying an injury and coach Roberto Mancini had used all his substitutes.

Inter, who seemed invincible for much of the season, went into Sunday's match looking for a win to steady nerves after picking up just two points from their last three matches.

Mancini's men also wanted to make up for the disappointment of suffering their first league defeat of the season on Wednesday, losing 3-1 to Roma.

By winning the championship with five games to spare, Inter have matched the record set by Torino in the 1947/48 season and equalled by Fiorentina in 1955/56.

It is the club's 15th scudetto, but it is the first time fans have seen Inter claim the trophy on the pitch since 1989.

Last year Inter were awarded the scudetto in July after the season was over when a sports tribunal revoked Juventus's title win in the fallout from the country's match-fixing scandal.

Roma travelled to Bergamo without defender Philippe Mexes and midfielders David Pizarro and Mancini, all suspended, and injured captain Francesco Totti.

Atalanta's Cristiano Doni headed in a superb cross from Brazilian Adriano Ferreira Pinto in the 37th minute and Riccardo Zampagna made it 2-0 just before halftime with a fine lob.

Simone Perrotta scored Roma's goal in the 19th minute of the second half.

Lazio (57 points) lost 1-0 at home to Fiorentina and now have AC Milan (56), who beat Cagliari 3-1 on Saturday, breathing down their neck for third place. Adrian Mutu's 15th goal of the season ended Lazio's 15-match unbeaten run.