Ancelotti successfully guided the Blues' to the Premier League and FA Cup Double this season, however Fergie is adamant that Mourinho is the better manager.
Fergie told French newspaper L'Equipe: "Jose [Mourinho] is an intelligent guy. Each time he speaks to the media, he galvanises his team. He has a tremendous effect on his players.
"The Chelsea of today have not rediscovered this unshakeable faith, even if they have won the title.
"With Mourinho, I understood after two Chelsea title wins that I had to adapt my preparation for my team to be competitive earlier in the season.
"I could not allow myself to let Chelsea get away. The Mourinho challenge was one of intelligence, of confidence in one's self. I had to pick up this challenge."
Fergie's comments come just days after Mourinho also played down Ancelotti's achievements in comparison with what the 'Special One' did in his time in English football.
"I'm happy Chelsea won the title. But please don't compare this Man United with my Man United," said the Inter manager.
"Don't compare this Arsenal with my Arsenal. My Arsenal was a team that won the league without defeat in 2003-04.
"Don't compare this Liverpool with my Liverpool. And don't compare this Premiership with my Premiership."However, the United boss also admitted that despite having to raise his game for Mourinho, the current Inter coach is not the most difficult opposition manager he has faced in his illustrious career at Old Trafford.
Fergie, 68, added: "Mourinho is not the hardest opponent I have had in my time at United. He only stayed three years in England.
"[Arsene] Wenger, over time, and [George] Graham were tougher rivals. It was hot stuff between United and Arsenal until three or four years ago."
Graham led Arsenal to title glory both in 1989 and 1991, while Wenger achieved the Double in both 1998 and 2002 and the Premier League with his unbeaten Invincibles in 2004.
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