Ferguson insists March 1 is when the Premier League will be decided as United face champions Chelsea at Stamford Bridge.
But after this point at Spurs put United top of the table on goal difference, Fergie pinpointed Chelsea as the big one.
"It's going to be an exciting run-in, a real thrilling end to the season as five clubs are at the top.
"All five teams contesting the title have chances and it makes it interesting for neutrals. Tottenham are not out of it, and are improving their chances each week.
"We have games in hand but you have to win them. It's all about keeping your nerve and at White Hart Lane defensively we kept ours."