The Red Devils stifled Liverpool's attack in a lacklustre game, which ended in a goalless draw between the arch rivals.
Jurgen Klopp's side were billed as favourites ahead of the match after taking points off Arsenal, Tottenham Hotspur and Chelsea earlier in the season, but they managed just three shots on target against United.
After the game at Anfield, Mourinho told Sky Sports News: "We knew it would be very difficult for them to score a goal and we thought we'd score the goal to win the match. We tried to start strong in both halves but they are a good team.
"But they're not the last wonder of the world like you (the media) try to say they are, but they are a very good team."
Three points separate the North-West rivals, with Liverpool fourth in the table and United seventh.