LONDON (AFP) - Chelsea boss Rafael Benitez, one of Alex Ferguson's bitterest rivals, led an avalanche of warm tributes to the Manchester United boss who shocked football by announcing his retirement on Wednesday.

Ferguson and Benitez often clashed when the Spaniard was coach at Liverpool.

At one infamous pre-match press conference in 2009, Benitez even pulled out a sheet of paper and read out a list of accusations about Ferguson's conduct.

But, four years on, Benitez preferred to concentrate on the positive legacy of the 71-year-old Ferguson's 26-year Old Trafford legacy.

"I have always liked to compete against him as a manager," said Benitez ahead of his team's Premier League clash against Tottenham on Wednesday. "As a person, I wish him health in his retirement and I hope he enjoys his football in a different way."

Spurs boss Andre Villas-Boas said Ferguson has left a legacy to be enjoyed by all inside the game.

"It's sad and surprising news. The EPL has lost one its most charismatic managers," said the Portuguese.

"He is the reference point in terms of coaches and in terms of being a successful manager. He is also a great human being.

"We will miss his charisma and dedication and passion. It's a legacy we can cherish. I hold him in high esteem."

Meanwhile, Rio Ferdinand hailed Ferguson's "work ethic".

"The bosses (sic) work ethic, his desire to win + to make us better players were unrivalled. Thanks boss," said United defender Ferdinand on Twitter.

David Beckham said Ferguson had been like a father to him.

"As I have said many times before the boss wasn't just the greatest and best manager I ever played under, he was also a father figure to me from the moment I arrived at the club at the age of 11 until the day I left," said Beckham, now with French giants Paris Saint-Germain.

Gary Neville, who along with Beckham and Paul Scholes was one of "Fergie's fledglings" - the youth system players who graduated into the first team - said he was proud to have worked with the "greatest manager of our time".

Bobby Charlton, one of the United directors who appointed Ferguson in 1986 and who persuaded the club's board to stick with the manager when results were going against him four years later, said Ferguson's dedication had been exceptional.

"He would get up in the middle of the night and travel 300 miles (482km) if he thought there was a schoolboy he could sign. He loves the game and we at the club have had nothing to do really," said Charlton, United's captain when they won the European Cup for the first time in 1968.

Fifa president Sepp Blatter said the sport may never again see a reign like Ferguson's at United that spanned 26 years and an astounding 38 trophies, including 13 Premier League titles and two Champions League triumphs.

"His achievements in the game place him without doubt as one of the 'greats'," Blatter said on Twitter.

"Will his longevity at the top ever be repeated?" Ottmar Hitzfeld, manager of the Bayern Munich side beaten in dramatic fashion by United in the 1999 Champions League final, said Ferguson's successor - widely tipped to be Everton's David Moyes - "will automatically be measured on Ferguson's success".

British Prime Minister David Cameron, a supporter of Premier League strugglers Aston Villa, tweeted: "Sir Alex Ferguson's achievement at #MUFC has been exceptional. Hopefully his retirement will make life a little easier for my team."

But Alex Salmond, Scotland's First Minister, said his fellow Scot's record at his previous club Aberdeen - rather than the success he had at United - was the real proof that he was an all-time great.

While at Aberdeen, Ferguson won the Scottish league three times, in 1980, 1984 and 1985, breaking the dominance of Glasgow giants Celtic and Rangers, who between them have monopolised the title ever since.

"I still think the greatest test of a real football manager is the ability to win the biggest prizes with unfashionable sides or less powerful teams," Salmond told Agence France-Presse.

"Winning the European Cup Winners' Cup with Aberdeen in Gothenburg (in 1983) is the indication that what we're talking about here is one of the all-time great football managers."

Current Scotland manager Gordon Strachan had the unusual experience of playing under Ferguson at both Aberdeen and United, as well as when he was in caretaker charge of the national side at the 1986 World Cup in Mexico following the death of Jock Stein.

"It really is the end of an era. Sir Alex Ferguson is a force of nature in world football and it truly was an honour to be managed by and to work with the best manager ever," said Strachan.