Mourinho’s former club have a 10-point lead at the top of the Premier League, and his first trip to Stamford Bridge as United manager ended in a 4-0 thrashing in October.
United return to London for Monday’s FA Cup quarterfinal, ahead of which Mourinho appeared to take a dig at Chelsea manager Antonio Conte’s tactical approach.
He told the Football Focus programme: “I’m not surprised [by the success]. I’m surprised with the way they play.
“I’m surprised because I thought they were demanding a different kind of football.
“I think they are very good defensively and I think they have fantastic players to be a counter-attack team and to kill opponents with three or four players.”
Chelsea, with Tottenham, have the best defensive record in the league — conceding just 20 goals in 27 games — and also possess the second most potent attack, with their 57 goals just one short of Liverpool’s total.
That tally was helped by the four they scored against United in October, a game that ended with Mourinho taking exception to the way in which Conte geed up the home crowd late on.
But the United boss stressed: “I’m not looking for revenge. I’m not looking for anything wrong or bad.
“If it’s different [playing Chelsea], it’s different in a positive way.”
United won the EFL Cup last month, and Mourinho stressed that he wanted more glory, adding: “That [the EFL Cup] is good, but I would lie if I say I think it is enough for us.”