Inter secured their 18th Scudetto at Siena in a game that had their fans biting their finger nails. Despite plenty of opportunites, it took until the second-half for the giants to open the scoring and win their fifth consecutive championship.
Diego Milito scored the lone goal of the match and sparked the celebration for the Milan giants as they added to their trophy cabinet having won the Coppa Italia already and could possibly claim the treble if they take the Champions League on May 22.
The visitors started the day knowing a win would guarantee them the title, regardless of what happened in Verona between Chievo and Roma.
Siena already knew they were going down to Serie B, but had the chance to play spoiler against the league leaders and stop them from winning Serie A. Coach Alberto Malesani opted for a lone forward in Massimo Maccarone in a counter-attacking 4-1-4-1 formation.
Meanwhile, Jose Mourinho saw the return of Wesley Sneijder from injury. Marco Materazzi and Mario Balotelli retained their spots in the starting XI from last weekend's victory over the Flying Donkeys.
The hosts actually had the first chance as a defensive mix-up saw the ball finish on the foot of Albin Ekdal in the box, but he somehow poked wide from a promising position.
Balotelli nearly gave the Nerazzurri the lead on 13 minutes, a long cross missed the head of Thiago Motta and the teenager volleyed wide from close range with the goalkeeper frozen.
A minute later, Milito was sent through and flicked past the goalkeeper, but the angle worked against him and the ball trickled just wide.
The Beneamata were patient in looking for openings, holding on to possession, and after neat interchange on the edge of the box, Maicon crossed to the far post, Balotelli headed back across the face of goal, but Gianluca Curci made a fantastic reaction stop on Milito's point-blank range header.
Again the Robur 'keeper was on his toes to deny Walter Samuel's header following a corner after a short delay in the match when Emilson Cribari was left stunned when blocking a cross with his face.
On 35 minutes, Samuel Eto'o did well to direct a Maicon cross on goal, but once again Curci palmed away, frustrating the treble hopefuls.
Siena finally showed themselves as an offensive force with Massimo Maccarone's strike from distance requiring an acrobatic save from Julio Cesar. At the other end, Balotelli's overhead kick smashed the crossbar as the score remained 0-0.
Midfielder Mato Jajalo skinned Javier Zanetti, but buckled under the pressure and dragged his shot wide from just inside the box. With news filtering through that Roma were two goals in front of Chievo, the Nerazzurri's grasp on the Scudetto was slipping as the half-time whistle blew.
Knowing they needed a goal, Mourinho's men were pressing higher at the start of the second-half and a one-two between Maicon and Balotelli saw the Brazilian break into the area, but his shot was deflected away at the last second.
A trademark Zanetti run setup Milito, but his vicious shot from just outside the area was finger-tipped over the bar by the in-form Curci. 'The Special One' went with an all or nothing attitude, throwing on Goran Pandev for Thiago Motta.
The pressure finally told on 57 minutes. Zanetti once again slalomed through the defence and laid off for his compatriot Milito, who controlled and slid the ball past Curci.
Robur captain Simone Vergassola tried to find an equaliser, but Julio Cesar had little trouble pouncing on his daisy cutter from 25 yards, as playmaker Sneijder came off for Cristian Chivu.
Substitute Dejan Stankovic hit the crossbar with a volley with 15 minutes remaining, poking at Diego Milito's bouncing assist on the edge of the area. Pandev did find the back of the net, but was offside when tucking home a rebound.
The Tuscans almost found a spectacular goal when Rosi's whipped in cross-shot just missed the far corner as the clock ticked down on 83 minutes.
However, the Coppa Italia winners held on as coach Mourinho won his second title in Serie A for president Massimo Moratti's club, coming on top in a very close race, two points ahead of the Giallorossi.