However, Mourinho's selection of the diminutive Spain international whom he sold to United in the first place—when he was manager of Chelsea in 2014—is not his only surprise move. The use of Marouane Fellaini, the current centre-back pairing and Antonio Valencia have all been met with raised eyebrows and quizzical looks.
It's a few games into the season, and it is clearly working—for now, at least. Let's take a more in-depth look at what he is doing and why.
The Juan Mata Question
A great deal of brouhaha surrounded Mourinho's decision to take Mata off after bringing him on as a substitute in the Community Shield.
The manager explained his case simply in the post-game press conference. First off, he felt he needed to make a tactical substitution to break up the impetus of Leicester City's attacks.
Secondly, given Leicester were firing balls into the box as often as possible, including their goalkeeper in attacks and generally making sure they launched the entire kitchen sink at United's back four, Mourinho did not want to lose any height from his team. Mata was the smallest player on the pitch, so taking him off made sense.
Any merit the "this is Mourinho secretly trying to break Mata's spirit" argument may have had was swiftly dispelled by the manager's surprising decision to include his former Chelsea charge in the starting XI of both of his first two Premier League games.
Not only that, but Mata featured in the right-wing berth that seemed a logical impossibility when Mourinho took over. Previous expectations were being reset. Indeed, Duncan Castles of the Daily Record wrote on 15 August:
Mata has impressed Mourinho with his willingness to follow tactical instructions both more demanding than those asked of him by Louis van Gaal, and requiring him to operate away from the Spaniard's preferred No. 10 role. "Jose loves the guy," a close friend told The Daily Record. "He works well and is a good player. Maybe not for 90 minutes, but very good for 60 minutes."
It may be unfair to suggest Mourinho's requirements are more demanding than Van Gaal's were. Indeed, Muhammad Butt of Squawka cited Van Gaal's influence on Mata, turning him into the hardworking, tactically disciplined wide man he has become:
So other than a newly discovered work rate and a propensity to put up defensive numbers—he is averaging 2.4 tackles, 1.2 crosses blocked and 0.6 passes blocked per 90 minutes this season—why is Mourinho picking Mata?
The player he is most obviously keeping out of the side is Henrikh Mkhitaryan. The Armenian showed flashes of brilliance in his debut cameo at Old Trafford on Friday night, and Mourinho praised him after the game.
Perhaps the manager does not think he is quite ready for Premier League action. Perhaps it is a question of squad-rotation politics and confidence management. Mourinho brought Mkhitaryan to the club, and the newcomer should have no cause to doubt how the manager sees him. Mata's history with his new boss is much different.
Giving him a few games now makes it clear he is in his plans.
Mata scored a goal upon chasing down a lost cause at Bournemouth and nearly provided an artful assist for Zlatan Ibrahimovic against Southampton, a deft flick of a header from a Paul Pogba dink into the box that Ibrahimovic almost bicycle-kicked towards goal.
That was one of the average of 1.8 key passes per 90 minutes Mata has made in the nascent United season.
Mkhitaryan will, presumably, become an important part of Mourinho's side as the season develops. On merit, it should be Wayne Rooney rather than Mata who makes way, but politics may render that tricky. However, Mourinho's surprise decision to turn to Mata is paying off.
At this point, a small note of caution should be sounded—it remains possible that Mourinho is putting Mata in the metaphorical shop window. But the player is still popular with large sections of the Old Trafford support and has plenty to offer the team. It would be good to see him stick around.
Blind and Bailly
During pre-season, Jamie Jackson reported for the Guardian that Chris Smalling and Phil Jones had been told they were to be Mourinho's first-choice pairing at centre-back. However, Daley Blind and Eric Bailly have occupied those positions for the season's first two games and are doing a sterling job.
Smalling suffered a pre-season injury, and Jones has been rendered peripheral by just how ready for the big time Bailly is. Ander Herrera told MUTV (h/t the club's website):
He’s so, so strong, he’s quick and he’s a very smart player. He doesn’t take risks, so that’s important for us because we know when we have the ball, or when he has the ball, he is not going to put the team under trouble.
When the opponent has the ball we have a very quick player, we can press up because the space is going to be covered by him. He’s very good in the air, very energetic, with every ball in-between he goes like crazy so he wins a lot of balls.
And Castles wrote of Blind in the Daily Record:
Blind, who at 1m80 [5'9"] is one of the smallest individuals ever to start in the centre of a Mourinho defence, has earned his new manager's trust with his attitude to a training regime radically different from Van Gaal's, his tactical intelligence, and a series of "fantastic" performances alongside new signing Eric Bailly.
Weaknesses exploited by Blind's opponents in his first two campaigns in English football have been countered by strengthening the back four's protection from midfield plus other strategic changes that include a switch from man-to-man to zonal marking.
United have conceded once in two games—though Southampton had chances—so for the most part, this is working.
A tough question will be asked of the manager when Smalling is back to full fitness. It is not yet clear that he should automatically get his place back in the side. He could replace Bailly, which would seem an odd move, given how exceptional the Ivorian has been. He could replace Blind, but the balance in the partnership might not be as natural.
Whatever Mourinho decides, the surprise centre-half pairing is doing the job.
Fellaini and Valencia Reborn
When asked about Fellaini's renaissance after the Southampton game, Mourinho cited a phone call. He said he had assured Fellaini of his place in the side and has made a deliberate PR push to help restore the player's reputation among the fans.
The Belgian has hardly put a foot wrong since he gifted Leicester a goal during the Community Shield clash at Wembley Stadium.
And Valencia has been on fire since Mourinho took over—assist after assist in pre-season has been followed into the season with barnstorming runs down the right flank. He looks unafraid to take on his full-back for the first time since the 2011/12 season, when he won Player of the Year for United.
These are individuals playing with confidence, surely the effect of good man management. The psychology of the situation is intriguing and speaks to just how important a top-level manager can be to a side. Not only has Mourinho's presence allowed United to attract world-class talent, but he is getting the best out of less obviously gifted players, too.
Blind, Mata, Fellaini and Valencia all seemed like candidates to be moved on once Mourinho arrived, but they have been integral to his first team. It has made for a fascinating, successful start to the season.
Plenty of surprises remain in store. Some will presumably be less effective than the shocks the manager has sprung so far. For now, almost everything Mourinho touches is turning to gold. The honeymoon period is in full swing, everything feels fresh and exciting, and it is enjoyable to watch.
Tougher times lie ahead, but for now, United fans are enjoying the ride.
Quotations obtained firsthand where not otherwise stated.
Advanced data per WhoScored.com.