It was one of the biggest transfer shocks in recent memory. Arsenal forward Alexis Sanchez, for months linked with a move to Manchester City with his contract expiring in the summer, moved to Premier League rivals United in a swap deal with Henrikh Mkhitaryan.
City pulled out of the race as Jose Mourinho got his man, while even Arsenal boss Arsene Wenger was happy, saying: "We lose a world-class player and we gain a world-class player."
How did the deal come about? ESPN FC's club correspondents share their insight into the transfer.
MANCHESTER UNITED: Mkhitaryan the key to beating City to Sanchez
Senior Manchester United sources were insisting as late as November that the prospect of doing any major business in January was slim. It was described as an "opportunistic" market, but the chance to bring Sanchez to Old Trafford was an opportunity that, in the end, they could not turn down.
Sources told ESPN FC that United were never really in the running for Sanchez in the summer, but when his £55 million move to Manchester City broke down on Aug. 31 they asked to be kept informed about the Chilean's situation. United's stance on transfers is that they are always interested in the best players in the world if they become available and for Mourinho and chief executive Ed Woodward, Sanchez fell into that category.
Even well into January, United believed Sanchez would sign for Pep Guardiola's side, though sources said they would look to take advantage of City believing they had all but tied up a deal.
Once Sanchez made it clear to Arsenal that he was determined to leave in January, combined with Wenger's insistence on having a replacement, United felt they had a chance.
Sources told ESPN FC that Wenger initially asked about the availability of Anthony Martial -- an enquiry that was swiftly knocked back by United -- yet United felt Mkhitaryan (33 days younger than Sanchez, with two years left on his contract, but out of favour at the time) was closer to Sanchez's value with only six months left on his contract. United were also aware that Wenger had tried to sign Mkhitaryan from Borussia Dortmund in 2016 before he eventually chose Old Trafford.
Sources said that once it was agreed Mkhitaryan would be part of the deal, Arsenal also wanted a further cash payment before being negotiated down by United to a straight swap.
Mkhitaryan himself, at first unsure about a move to the Emirates, did not officially agree to sign until Jan. 20, two days before the deal was announced. He had been told by United that they were confident of signing Sanchez even without his involvement and consequently he would find first-team opportunities even harder to come by. In the end, he was persuaded and United believe they got a "fair" deal -- improving their squad with Sanchez, while Mkhitaryan got a pay rise and a chance to play more often at Arsenal.
Defending Sanchez's high basic wage of around £350,000-a-week, sources said the club could pay him more as it was a free transfer. United also insist they have not broken the bank for the 29-year-old and he fits comfortably into the wage structure -- though reports suggest he beat Paul Pogba to become the top earner at the club and, indeed, the Premier League.
In essence, it was a worthwhile outlay to land one of the best players in the world and the club believe they got a fantastic deal. -- Rob Dawson.
ARSENAL: Sanchez's bad attitude and a readymade replacement made the difference
For Arsenal, getting a player in return for Sanchez was always the preferred outcome. Wenger had been adamant that the Chilean wouldn't be allowed to leave unless a replacement could be brought in, and the reported £92m deadline day deal for Thomas Lemar which collapsed in August showed how tricky (and expensive) that could be. The club knew that even if they got £30m for Sanchez -- about the best they could hope for with his contract running down -- they'd have to spend much more than that on another player of similar quality.
"We were in the position where the player had no value in three to four months, so that is of course important in our decision," Arsene Wenger said last week when asked by ESPN FC about the importance of getting a player instead of cash for Sanchez.
Sources said that in his talks with Manchester City this summer, Arsenal CEO Ivan Gazidis had raised the prospect of including Raheem Sterling in a possible deal. However, he was quickly told that wasn't an option and a swap was never seriously discussed with City ahead of the January window -- especially given the player's excellent recent form.
That's why United quickly jumped into pole position once Mkhitaryan was offered up as counterweight.
Arsenal had identified Bordeaux winger Malcom as their No. 1 target while a cash deal with City looked most likely, sources said. But that interest cooled as soon as United stepped in, with Mkhitaryan seen as a player in his prime who could contribute immediately, while Malcom is still a raw prospect and would cost more than they were getting for Sanchez.
Sanchez had made it very clear to the club in the summer that he wanted to leave, and he returned to the club in a foul mood after that deadline day move to City collapsed on the same day that Chile lost a crucial 2018 World Cup qualifier. Still, Wenger was holding out hope that the winger's unhappiness wouldn't show on the pitch and that his winning attitude would guarantee good performances.
Sources said that had Arsenal been in a title fight, the club would have been ready to keep hold of both Sanchez and Mesut Ozil until the summer even if it meant losing both for free. But a poor start to the season saw those hopes disappear and Sanchez's frustrations returned just as quickly.
Over the last couple of months, Sanchez's teammates had grown increasingly frustrated with him, sources said. His attitude around the training ground and poor performances during games created a rift with some players. During the 1-1 draw at Southampton, Jack Wilshere openly chastised the forward on the pitch, and it was reported by multiple outlets that several players continued their remonstrations in the dressing room after the final whistle.
While Wenger kept insisting everything was fine -- even after some players didn't celebrate with Sanchez after he scored at Crystal Palace in December -- the disharmony in the team added to the sense that the club were better off letting Sanchez go in January.
In the end they did and last week, midfielder Mohamed Elneny showed just how he felt about Sanchez's departure when he wrote on Twitter after the Carabao Cup win over Chelsea: "Now there are players fighting every minute for the logo and the fans." -- Mattias Karen
MANCHESTER CITY: For once, money was an object; Sanchez was not a priority
City's hierarchy including manager Guardiola, chairman Khaldoon al Mubarak, chief executive Ferran Soriano and director of football Txiki Begiristain held a meeting on the morning of Jan. 15, which is when they decided to end their pursuit of Sanchez, sources told ESPN FC.
They considered the package of transfer fee (around £35m), signing on fee, salary and agent's fee too expensive and believed it could even amount to more than the deal they had agreed with Arsenal in the final days of the summer transfer window before it collapsed.
Sanchez was never seen as a priority in the January transfer window but City decided to step up their interest when the player indicated he was desperate to leave the Emirates and was unwilling to wait until the summer.
A decision to walk away from the deal was helped by a good diagnosis on Brazilian striker Gabriel Jesus, who had suffered a knee ligament injury over Christmas but is set to return in early February. And City decided to prioritise other positions with Vincent Kompany's persistent injury problems affecting his reliability, while there is also concern over the quality of Eliaquim Mangala.
With left-back Benjamin Mendy out with a cruciate knee ligament injury and Fabian Delph also suffering a setback, City instead opted to move for a left-footed central defender which is why they renewed their interest in Athletic Bilbao's Aymeric Laporte.
City were in the process of renewing contracts for senior players David Silva, Nicolas Otamendi, Fernandinho and Kevin De Bruyne, and Sanchez's wage demands would have seen him earn significantly more than those. Guardiola wanted to reward the players that had performed so well in the first half of the season and didn't want to risk disrupting the dressing room by bringing in a new player that could unbalance the squad.
De Bruyne did not seem overly disappointed after the move broke down saying: "He chose United. OK, there are a lot of good players. If they want to come, they want to come, and otherwise we will do it with our team."
The Belgium international's new five-and-a-half year contract was announced at exactly the same time as Sanchez and Mkhitaryan's swap deal, but City sources said that was purely coincidence.
Clearly, the club took the decision to focus on what it already had -- which isn't too bad by the way -- even if that meant a rival got to strengthen.