Samuel Eto'o scored a hat-trick as Chelsea moved two points behind leaders Arsenal and a point behind second-placed Manchester City in a result which leaves seventh-placed United 14 points adrift of the summit.
Mourinho thinks David Moyes will be unable to overturn the deficit to all three teams in the remaining 16 games of the season and that United will not be able to retain the title Sir Alex Ferguson won before his retirement in May.
The Chelsea boss said: "It's a 14-point difference. And 13. And 12. Can they recover to one of these teams? They can.
"But to recover to three of them, it needs three teams to have almost a collapse.
"For the title it will be difficult for them. What I hope to do is they beat all of them (Chelsea's rivals) to finish top four and they beat all of them."