The finishing touches to the deal were made on Monday and an announcement that the two 29-year-olds had traded places was made at 6pm.
Speaking for the first time as a United player, Sanchez said: “Since I was a young lad I’ve always said that my dream was to play for Manchester United, and I’m not just saying that because I’m here now and today it’s come true.
“I always said as a kid that I’d like to play for United and I once spoke to Sir Alex Ferguson about it. We chatted for around 20 minutes and I told him that my dream was to come here to Manchester United.
“It really is a massive club, very powerful, and so now, when I got the opportunity to come here, I looked at the badge and my hairs just stood up on end because it’s a powerful club and the biggest in England.”
Yet despite saying he’s waned to play for United since he was young, Sanchez then appeared to admit he didn’t even know who had donned the No 7.
He told MUTV: “When they told me that Cristiano, Eric Cantona, David Beckham had all worn it, just thinking about that number seven sets you off dreaming in your head with ideas about lifting the Champions League trophy and winning the Premier League title.
“So yes, I’m fulfilling a dream and I hope to give my very best and win many trophies at this club.”
United’s new signing, who missed Arsenal’s win over Crystal Palace on Saturday while negotiations over a switch continued, posted a departing message on Instagram where he took aim at ex-Arsenal players that have been critical of him.
Though his social-media post did not reference anyone directly, Sanchez wrote: “There are people (former club players) who have spoken with no knowledge of what happens inside the club and cause damage.
“I must say I always gave 100%, until the last day, when I asked to the Mister (Arsenal manager Arsene Wenger) to be in the team, because I wanted to be a contribution.”
Martin Keown, a former Gunners defender, had called Sanchez “the biggest mercenary in football”, with suggestions the Chilean forward will earn £500,000 a week at Old Trafford.
United’s rivals Manchester City had tried to sign Sanchez in the summer and revisited the possibility in this window only to pull out due to the rising costs.
Arsenal wanted £35million for a player out of contract in the summer and United’s willingness to meet Sanchez’s wage demands and use a makeweight in Mkhitaryan, who is valued at the Gunners’ asking price, allowed a straight swap to take place.
7 GREAT MANCHESTER UNITED NUMBER SEVENS
Johnny Berry (1951-58)
Berry was one of the Busby Babes who was forced to retire due to injuries he sustained in the Munich air disaster. However, he did manage to win three league titles during his eight years at the club and was regarded as one of the best young players in Britain.
George Best (1963-74)
Not exclusively a number seven. Indeed, Best probably wore number 11 more often. However, on the greatest night of his footballing life, when United defeated Benfica in the 1968 European Cup final at Wembley, he was wearing the seven shirt. He also won two Division One titles with United.
Steve Coppell (1975-83)
He may not quite have the profile of some of the others to wear the shirt but Coppell kept the number seven for six years on his arrival at United. He wore it in three FA Cup finals, including the 1977 victory over Liverpool.
Bryan Robson (1981-94)
Coppell switched when Robson made his British record move from West Brom in 1981. The inspirational midfielder became the first player to captain three FA Cup-winning teams, also led United to the 1991 European Cup Winners’ Cup, and the League Cup before getting his hands on the first Premier League title in 1993.
Eric Cantona (1992-97)
When the Premier League made squad numbers mandatory at the start of the 1993-94 campaign, Cantona was handed the shirt. The Frenchman had already earned himself a place in United folklore and went on to win four titles and two FA Cups, scoring the winner against Liverpool in the 1996 final, when he had also been named captain.
David Beckham (1992-2003)
After Cantona’s sudden retirement, Beckham jumped at the chance to switch from 10 to seven. It meant he was the player who wore the shirt during the 1998-99 treble-winning campaign, and the subsequent titles in 2000, 2001 and 2003.
Cristiano Ronaldo (2003-09)
Beckham’s profile meant there was always going to be a spotlight on who inherited the shirt and Ronaldo proved to be the perfect successor in more ways than one. During a six-year stint in which he won three league titles he was also crowned World Player of the Year in 2008 for his phenomenal 42-goal contribution to a campaign in which United also won the Champions League.