Brazilian star Kaka set up Filippo Inzaghi for Milan's first and then scored the team's second shortly after, with Julio Cruz's long, curling free-kick the only reply from Inter.

The outcome, coupled with Roma's victory at Sampdoria, cut Inter's lead over the Romans to just three points with two rounds remaining.

But Mancini said: "Without a doubt on Sunday at Siena, we will win the Scudetto."

Milan went close to scoring on the stroke off half-time when Inzaghi got his head to a Clarence Seedorf cross but he wasn't able to get the shot on target.

"Milan played better in the first half and we offered very little," Mancini said.

"We then conceded a Filippo Inzaghi goal and then we made a mistake which we don't usually do and which allowed Kaka to score.

"Mistakes happen and you have to accept them, but certainly conceding the second goal shortly after was difficult for us."

Inter crashed to a heavy defeat at Lazio on the final day of the 2001/2 campaign to allow Juve to win the championship.

But Mancini insists there is no reason to worry this time around.

"We knew it was going to be difficult and although we scored, we knew that this game could go either way," he said.

"I had that out of the three games we had remaining, we could have lost today's game and that was the case.

"I didn't expect Roma to lose points in Genoa against Sampdoria, either."

Mancini then offered an excuse as to why his team has not already clinched the crown.

"I think the biggest problem for us has been the injuries we've had this season," he said.

Milan's players, meanwhile, were all smiles as they walked off the pitch because the club climbed above Fiorentina and into fourth place - the final qualifying spot for the Champions League.

"We have given ourselves a great present and results have gone our way as we are fourth," Milan coach Carlo Ancelotti said.

Indeed, Fiorentina, who lost 4-2 on penalties in midweek to Rangers in their UEFA Cup semi-final second leg, followed that up with a 2-1 defeat at Cagliari on Sunday.

"Now we depend on ourselves," Ancelotti said.

"We knew we had to play a great game in order to win this derby and that is what we have done, for this game was crucial and my players showed great determination from the start to win this encounter.

"Inter played a prudent game and they were content to sit and wait for us and that has allowed us to construct our play and control the game," he said, before agreeing with Mancini's prediction.

"Inter just need a win to claim the Scudetto and I think they will win it next weekend," he said.