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Manchester City manager Roberto Mancini claims it has been an honour to compete against Sir Alex Ferguson - the best manager of his generation - over the past three years.
Mancini's arrival at the Etihad Stadium in December 2009 has coincided with a resurgence in the rivalry between City and Ferguson's Manchester United at the top of the Barclays Premier League.
City memorably beat United in the 2011 FA Cup semi-finals and then pipped them to the Premier League title in dramatic circumstances last year, a season in which they also thrashed their neighbours 6-1 at Old Trafford.
United have reasserted themselves by reclaiming their league crown in emphatic fashion this season, an achievement which has proved Ferguson's final act as United boss with the Scot now stepping down after more than 26 successful years.
Mancini said: "For me, it has been a great honour and pleasure to compete against Sir Alex for three years.
"It was a great honour to beat him in Old Trafford and I wish him good luck for his future. I don't know for which reasons (he has retired).
"Everyone can have his opinion but one manager who stays for 27 years in the same club and won every trophy for 27 years - it is an incredible situation.
"I don't think there will be another manager like him.
"It is difficult to say Sir Alex is the best (ever) but he is the best in the last 27 years."
Ferguson's retirement will leave a big hole for his replacement David Moyes, the current Everton boss, to fill but Mancini knows he cannot expect the balance of power to shift back in City's favour.
The Italian said: "I don't think this. At a top club, a big club like United, you can change the manager.
"Sir Alex built this team but it is a big club with a big history and I don't think it will change something."
Mancini, who added that he had sent Ferguson a message since he announced his decision, will now need to get the better of Moyes, a task he has struggled with when up against Everton.
Moyes' Everton sides have beaten City six times in their last eight meetings while the pair were also involved in a touchline scuffle three years ago.
Mancini, who is preparing his side for this weekend's FA Cup final against Wigan, said: "It is better we can talk about this if we can play the Community Shield against United next year."
When asked if Ferguson's decision had overshadowed the build-up to the Wembley encounter, Mancini said: "I don't know this.
"We talk about our final because for us this is more important.
"After we talk but we didn't know nothing about this decision."
Former England manager Fabio Capello was also gushing in his praise of Ferguson, but admitted he had been taken aback by the announcement due to a conversation he had with the Scot earlier this season.
The Italian said: "I met him a few months ago at the England Sports Centre and he told me he would carry on, so the news of his retirement surprised me.
"I called him yesterday and he told me he has decided to go now because there is too much stress nowadays. Always having to win something is very challenging, and he told me he wanted to go around the world with his wife.
"His secret is amazing. To have that strength and ability to change things and improve every year, and always have the same desire to win."
West Ham boss Sam Allardyce, who was still playing when Ferguson began his Old Trafford reign, cited the 71-year-old as a major help when he was cutting his managerial teeth in the 1990s.
"He has had huge influence on me," he said.
"I got to know Sir Alex when I was at Notts County when I was invited on to the LMA (League Managers' Association) committee.
"To get to the Premier League with Bolton and get to compete against him and build up a pretty good friendship with him... He has been a huge influence on me.
"I have been managing for 20 years now and a lot of that has been phone calls when you are in a pretty dark place in this game as a manager. You need some advice and you need to know who to turn to, and that solid advice would always come from Sir Alex if you rang him."
Harry Redknapp has been doing battle with Ferguson in the Premier League for the best part of 20 years and believes his retirement will leave a big hole in the game.
"He will be a great loss to the league and football," he said.
"He is a fantastic manager, but a top bloke as well who always had time for young managers if they phoned up - no matter what level they were at.
"He was always there for anyone and he was a big driving force behind the LMA. That shows you what he was about.
"I always spoke to him and enjoyed his company and he would have been a big influence on a lot of the younger managers.
"It was an amazing achievement what he did - taking over one of the biggest clubs in the world going through a difficult period and then started winning championships and everything else he could win."
And the QPR boss was also quick to praise the appointment of Moyes, who has spent the past 11 years building competitive sides on a limited budget at Goodison Park.
He added: "Great job for David - I couldn't be more pleased for him.
"He's the prefect choice and I think it is good that they have taken a British coach and have given him a chance. They have not just gone abroad but taken someone who has done his apprenticeship.
"It gives great hopes for everyone out there in all divisions.
"He has worked his way up the ladder and did a fantastic job at Everton."
Tottenham manager Andre Villas-Boas felt next season could be a critical one for United as they adapt to life after Ferguson.
"It's a big time for Manchester United, a completely different situation," the Portuguese said.
"They've appointed a great manager, a person full of charisma and passion for the game like David Moyes. I think the appointment is excellent but the transition from a manager who represented so much for that club is going to be very sensible. I believe that it will be a different story."
Asked if Moyes would be under instant pressure to produce results, Villas-Boas said: "I think Man United have a different philosophy. The first thing that comes out is the length of David's contract (six years), which is the type of security and belief that you need as a manager to work safely and properly.
"It will be a year of transition and I think they will give David all the time possible to establish his ideas and what he wants to move forward for the club."