Sir Alex Ferguson believes the Premier League title race is already down to two - and he would not be surprised if the two derbies prove crucial in deciding whether the trophy ends up with Manchester United or Manchester City.
The two clubs meet at the Etihad Stadium in the first meeting of the season on Sunday, with United hoping to increase their current three-point lead atop the table.
With third-placed Chelsea another seven points further back, Ferguson believes that an away defeat to City could prove decisive come the end of the campaign. United lost to City home and away last season, as Roberto Mancini's side ultimately clinched the title on goal difference.
"I think it is going to be close," Ferguson said of this year's title race. "With that gap over Chelsea, Arsenal and Tottenham it'll be difficult for the two of us to collapse and let another team in. I think it will be between the two of us."
On whether the two defeats in last season's derbies cost United the title, Ferguson added: "Without question. Particularly that 6-1 defeat we had [at home]. It turned things right around. It cost us."
Ferguson believes it is too early to say whether Sunday's game will prove similarly pivotal in the title race, noting that his side have overcome - and let slip - bigger leads than six points before.
"We've won the league after being 12 points behind, and we've lost the league after being 11 points ahead... so you can never be sure in this league," he added. "You can lose to anyone - we've lost to Norwich already - but that's the type of league we're in, that's a tough league."
Mancini claimed on Friday that United are favourites for the game, but the Scot believes the derby is almost impossible to predict.
"It's always full of surprises," he said. "You know it is going to be a hard game for us, but we're capable of beating anyone. We've proved it time and time again."