Chelsea and Manchester United beat the clock in the final minutes of the transfer window with the Blues breaking the British transfer record by signing Enzo Fernandez from Benfica.
On Wednesday morning, Chelsea confirmed World Cup-winner Fernandez completed his British record £106.8million transfer, after negotiations went to the final hours of a dramatic transfer deadline day.
Benfica were first to announce the signing overnight and Chelsea hailed Fernandez's capture on Wednesday morning.
"The Argentinian midfielder has completed his transfer from Benfica to Chelsea," said a statement on the club’s website.
It is understood that the 22-year-old undertook a medical in Lisbon on Tuesday evening as the clubs worked towards an agreement, with disagreements relating to the instalments in which the fee will be paid taking the deal down to the wire.
Fernandez becomes the eighth signing of a frantic window for the Blues, with a total January spend by owner Todd Boehly of around £318m.
Fernandez, who won the Silver Ball for best young player during Argentina’s triumphant World Cup in Qatar last year, has signed an eight-and-a-half-year contract, in keeping with the club’s policy this season of signing players on lengthy terms in order to spread their outgoings and remain within UEFA’s Financial Fair Play rules.
It takes the Blues’ spending since Boehly bought the club last May to more than £550m, though UEFA are set to close the loophole that has allowed for such a large outlay by limiting contract length to five years.
The Fernandez deal took Chelsea's spending since last summer past the €620m barrier and broke the previous British transfer record, set by Manchester City following the signing of Jack Grealish for £100m in August 2021.
Manchester United, meanwhile, completed their shock loan signing of Marcel Sabitzer with the Austria star saying "sometimes in life you have to make quick and important decisions".
The Red Devils made their move for the Bayern Munich midfielder after it emerged that Christian Eriksen would be ruled out until early May with the ankle damage sustained in the FA Cup win over Reading on Saturday.
Sabitzer, 28, who has played 68 times for Austria, has joined United on loan for the rest of the season.
"Sometimes in life you have to make quick and important decisions," Sabitzer told the United website.
"From the moment I heard about this opportunity I knew it was right for me. I am a competitive player; I want to win and help the club achieve its aims this season.
"I feel that I am at my peak as a player, and that I can contribute a lot of experience and energy to the squad.
"I am excited to start with my new team-mates and manager and to show my qualities to Manchester United fans."
It is understood that United defender Axel Tuanzebe is heading out to Stoke on loan.
Chelsea had earlier seen a midfielder leave with Jorginho joining Arsenal on an 18-month deal.
The 31-year-old Italy international moved across London after Arsenal had been keen to strengthen their midfield options following Mohamed Elneny's serious knee injury earlier in the month.
Jorginho told Arsenal.com: "I'm very excited for this new challenge, and I just can't wait to be on the pitch to be honest. Everything has happened so fast.
"I was a bit surprised, but I took the opportunity of this amazing challenge.
"It's an important shirt. It's an amazing club, a big one, and I'm really excited and happy to be here."
Manchester City full-back Joao Cancelo has joined Bayern Munich on loan for the remainder of the campaign.
Bayern's unexpected swoop for Cancelo is understood to include an option for the German giants to buy the 28-year-old Portugal international for €70m in the summer.
Cancelo said: "FC Bayern is a great club, one of the best in the world, and it's enormous motivation for me to now play alongside these extraordinary players in a team."
Tottenham announced the signing of Pedro Porro from Sporting Lisbon 10 minutes before the deadline.
The 23-year-old wing-back has signed on loan until the end of the season with an obligation to make the move permanent in the summer.
Spurs had earlier torn up Matt Doherty's contract to allow the Republic of Ireland full-back to join Atletico Madrid.
Doherty's departure was initially set to be temporary, but that would have taken Tottenham up to nine players out on loan and FIFA's limit is eight.
Djed Spence, another Spurs full-back, joined Ligue 1 side Rennes for the rest of the season.
Bournemouth completed a busy January with the deadline-day signings of Illia Zabarnyi and Hamed Traore.
Ukraine defender Zabarnyi has penned a five-and-a-half-year deal after leaving Dynamo Kyiv, while Ivory Coast midfielder Traore joins from Serie A outfit Sassuolo on an initial loan agreement which will become permanent in the summer for a further five years.
Nottingham Forest also had a frenetic finish to the window with three signings in the final hour or so before the deadline.
Veteran defender Felipe came in from Atletico Madrid, midfielder Jonjo Shelvey joined from Newcastle and goalkeeper Keylor Navas signed on loan from Paris St Germain.
Crystal Palace added to their midfield resources with Stuttgart's Naouirou Ahamada and Albert Sambi Lokonga, who has agreed a loan deal from Arsenal until the end of the season.
Fulham have signed Torino midfielder Sasa Lukic for a reported fee of around £9m.
Lukic, who joins his fellow Serbian international Aleksandar Mitrovic at Craven Cottage, has agreed a four-and-a-half-year deal, with Fulham holding an option to extend by a further 12 months.
Leeds saw Diego Llorente leave for Roma on loan until the end of the season with a view to a permanent deal, but signed a player for the future in 18-year-old centre-back Diogo Monteiro from Swiss Super League side Servette.
Leicester signed Australia defender Harry Souttar from Stoke on a five-and-a-half year deal, with Ayoze Perez joining Real Betis for the rest of the season.