Arsenal manager Arsene Wenger is surprised by the evenness of the Premier League title race this season.
Only 12 points separates Chelsea and United through 21 league games this season.
Wenger, whose team are fourth, said he was unable to remember such a closely-fought title race.
"It's the first time in 20 years that at this stage of the season you have six teams at the top," the Frenchman told UK newspapers.
"Chelsea still have a big advantage, but they're all doing well.
"You look around you and nobody is dropping off, so it's down to being consistent, keeping your nerve, focusing on your game.
"Now we go into Europe, into the cups, big games – who can maintain it? Honestly, nobody can tell."