Less than three weeks after the Premier League season finished with United six points ahead of Chelsea, the club said Thursday that it would sign Owen Hargreaves from Bayern Munich.
Sporting confirmed Thursday that Nani will move for 17.3 million pounds (US$34.3 million; EUR25.5 million), which is about what Hargreaves will cost. British and Portuguese papers reported that Anderson's transfer was worth a similar amount.
Liverpool manager Rafa Benitez said last week that clubs needed to move fast in order to add top players to their squads for next season, and United is doing just that.
United made just one big signing in the last offseason, paying Tottenham 18.6 million pounds (US$36.8 million; EUR27.4 million) for England midfielder Michael Carrick.
Calming fans' fears that the 2005 takeover by Malcolm Glazer had curbed the club's largesse when it came to competing for the best players, United is now spending on the scale of Chelsea and its billionaire owner Roman Abramovich and doing it quickly.
The 26-year-old Hargreaves had been linked to United for a year and is expected to line up with Carrick in central midfield, as he has done for England.
The Canadian-born midfielder was England fans' player of the year in 2006 after starring at the World Cup and should provide the defensive cover United has lacked in recent years.
The transfer fee for Nani is the biggest Sporting has ever received, and is almost 50 percent more than it got from United for Cristiano Ronaldo four years ago.
Ronaldo swept England's player of the year awards this season, scoring 17 goals to lead United to its first Premier League title in four years, and, like Ronaldo, Nani can play on either wing.
The 19-year-old Nani, whose full name is Luis Almeida da Cunha, may be an eventual replacement for the aging Ryan Giggs, who retired from international soccer with Wales this week to prolong his club career.
Born in the Cape Verde Islands, Nani made his league debut two years ago after taking Portuguese nationality. Noted for his long passing and shots, he made his Portugal debut in November and, with Ronaldo suspended and Benfica's Simao Sabrosa's injured, is likely to start Saturday's European Championship qualifier at Belgium.
He scored five goals made 29 appearances for Sporting last season.
The 20-year-old Anderson is a combative midfielder who may end up replacing Paul Scholes if he gets the work permit he needs to complete the move.
He has been called into Brazil's squad for next month's Copa America in Venezuela, but is already thinking about next season.
"I cannot wait to play in the same team as Cristiano Ronaldo, who is a great player, as well as Wayne Rooney and many more," Anderson said.
"Ever since I was a boy I always wanted to play for Manchester United and now that dream has come true. I am very happy."
United is still rumored to be searching for a striker to play alongside Rooney but knows it must spend wisely.
Chelsea had won two straight English championships before spending 57 million pounds (US112.7 million; EUR83.9 million) last year on Andriy Shevchenko, Khalid Boulahrouz, John Obi Mikel and Salomon Kalou - and signing Germany midfielder Michael Ballack on a free transfer.
It won England's FA Cup and League Cup, but failed to clinch its primary targets of Premier League and Champions League.