Leaders United have a one-point advantage over reigning champions and neighbours City, with Chelsea and West Brom breathing down their necks six points further adrift.
Many critics are already ruling out the title credentials of a spluttering Chelsea side guided by new interim boss Rafa Benitez.
But Ferguson said: "It's early-season. It's only the end of November, so I don't think you can be certain by saying it's a two-horse race at this time.
"Over the years, we've always hoped the top five, or top six, are all capable of winning the league but eventually it ends up being a two-horse race.
"Year after year it's been like that, when you look at the space between the top two teams and the rest last year, the gap between ourselves and City.
"The important thing is you look at yourself. You need to stay up there all the time and this is not an easy league to do that."
City boss Mancini echoed similar sentiments, adding: "I think Chelsea could win. In this moment I think it's a three-horse race but it's difficult to say.
"It's difficult to say this because the season is long and I think in February when the Champions League starts then everything can change."