Joint leaders in the league with Manchester City with 13 points from five games, United beat Everton 4-0 on Sunday and have defeated West Ham United and Swansea with identical score lines.
Mourinho, whose side drew 15 games last season as they finished sixth, was pleased with the "clear difference" in their style of play and the ability to push on for wins this season.
"I think the Premier League is becoming defensive... many teams try to play with five at the back plus two or three in the middle," he told the club's website (www.manutd.com).
"Two teams try to match each other and play the same system and it's 0-0 or 1-0."
United scored three of their four goals after the 80-minute mark against Everton as their opponents committed more players forward late on in search of goals.
"When you have a little bit more space, you try in the last part of the game and they (Everton) were losing 2-0 and they (came at us) more and gave us more spaces," he said.
"We played better and we score more goals."
Mourinho said his team must now shift their focus to the League Cup where the defending champions face Burton Albion in the third round on Wednesday.
"Every match is a different match and the next one, against Burton, who come on the back of an important result against a good team like Fulham," said the Portuguese manager.
"It will be another difficult match."