That is according to Gunners legend Martin Keown.
The former Arsenal centre-half feels Jurgen Klopp and Arsene Wenger's teams are too attack-minded.
United sit joint-top of the Premier League table alongside Manchester City, having conceded just twice so far.
Following six wins and a draw, United face their toughest test yet at Anfield on Saturday (12.30pm).
But Keown has been impressed by how Mourinho's side have managed to shut up shop in games.
And that will prove crucial to United pipping the likes of Liverpool and Arsenal to trophies this season.
"Kenny Dalglish is an ambassador of the club and I’m sure he wants to talk up the positive, attacking football that Liverpool are playing now," Keown wrote in his Daily Mail column.
"But, make no mistake, the late goals, sloppiness and lazy defending will be driving Jurgen Klopp mad.
"Arsene Wenger has not won a Premier League title since 2004.
"His Arsenal teams since have been committed to attacking but have not respected the defensive side of the game enough.
"I’ve said it time and again — the team which strikes the best balance will win the title.
"In their 1-0 win at Southampton, Manchester United showed they could grind out results. It may not always be attractive, but every player who has been part of a Premier League success knows they have to do it.
"In a league where Liverpool can thrash Arsenal and then be well beaten themselves by Manchester City in consecutive matches, it is as if people only seem to take notice if you win big.
"Jose Mourinho knows that the ability to win 1-0 is what will win you titles."
While Manchester United go to Liverpool, Arsenal travel to in-form Watford on Saturday (5.30pm).
A win for the Red Devils will see them go 10 points clear of the Reds after just eight games.
