Few could have imagined the woeful campaign that would follow Sir Alex Ferguson's 27-year reign coming to an end with a 13th league title.
United's seventh-place finish was their worst in the Premier League era and means they will be absent from European competition for the first time in 25 years.
Just to rub salt into the wound, neighbours Manchester City wrestled the title away from them on Sunday - a situation January signing Mata has vowed to put right next term.
"It's always nice to finish with a goal, and especially from a free-kick," he said after scoring in Sunday's 1-1 draw at Southampton.
"I will tell David De Gea to stay with me at the end of the training sessions so I can practise more.
"The goal helped the team to avoid a defeat in Southampton, although the score and our final position on the table is nothing we feel proud of.
"At United, if you don't win the Premier League one year you know you have to do it the next time, and we will get ready for that.
"I believe it's fair to congratulate Manchester City for winning the title
We will try to bring the celebrations to our side the next year."
Mata will undoubtedly play a key role in that title bid, with the Spain international settling in impressively after swapping Chelsea for United in January.
The 26-year-old has won the club's player of the month award in two of the three months since his arrival and is "looking forward to more".
It is Mata's compatriot that got the main award this term, though, with De Gea's fine form between the sticks seeing him collect the player of the year award - a crown made all the more special given no goalkeeper has won it before.
"The big prize was for De Gea and I was honoured to present it: United's player of the year, voted for both by the fans and the players," he posted on his official website, juanmata10.com.
"It's the first time that the trophy goes to a United goalkeeper and David deserves a lot of credit for that.
"He's got amazing qualities and he may become one of the best goalkeepers in the world - I believe so."
United are expected to name Louis van Gaal as manager this week, when the future of Sunday's opponents Southampton is also expected to become clearer.
England internationals Luke Shaw and Adam Lallana have reportedly been subject of bids from Manchester United and Liverpool, respectively, while manager Mauricio Pochettino's future remains the subject of much speculation.
The Saints boss is expected to talk about a new deal with the board on Monday, having overseen Saints' best ever Premier League season.
Southampton finished eighth with a points haul of 56 - an achievement particularly special to Rickie Lambert, who has been key in the club's rise from the League One doldrums.
"We were hoping for it and we believed in it and we've done it," the striker said.
"Not just this season, every year we've gone above and beyond, it's been amazing to be a part of, and that's just topped it off.
"I've given my all and I've absolutely loved playing with this group as they've come up over the last five years and I've loved every minute
It's the way we play - everything is a credit to Southampton Football Club."
Source : PA
Source: PA