Manchester United fans were treated to a stress-free night against League One side Shrewsbury on Monday as Louis van Gaal's men sailed into the quarter-finals of the FA Cup with a 3-0 victory.
While the struggling Premier League outfit were dominant throughout proceedings, they also got a helping hand from the referee after replays appeared to show that Mata's free-kick should have been disallowed.
Shrews' goalkeeper Jayson Leutwiler was left rooted to the spot as Mata's spot-kick casually sailed into the back of the net, making it 2-0. But that was only because his view was being completely obscured by three offside Manchester United players.
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As is always the case with the confusing offside rule, it was a matter for debate amongst fans and pundits after the final whistle, but Van Gaal admits that even he believed it was offside. That was until he saw FC Midtjylland doing the same thing in recent scouting trips.
Their Europa League opponents, who left them humbled last Thursday after a shock 2-1 defeat, practiced the same routine, leaving the Dutchman confused as to the rule. He admits he first sought confirmation from a referee before giving Mata the green light.
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"We have learned because we analysed FC Midtjylland and we saw they were doing that," the Dutchman told reporters.
"We thought it was always offside so we asked the referees and they said it’s not offside, you can do that. That’s why we have learned about the taking of the free-kicks. Today we scored and that’s good."
Here is the goal
Whether Mata's goal was or was not supposed to stand, the result would most probably have been the same. Goals from Chris Smalling and Jesse Lingard on either side of half-time added to Mata's free-kick to earn Manchester United a sixth round tie against West Ham.
However, it was not all good news for the Red Devils as Van Gaal confirmed that his team had suffered two more injury blows. Already with a lack of options up front, the former Bayern Munich boss revealed Will Keane will now be joining Wayne Rooney in the treatment room.
"It is unbelievable because also [Cameron] Borthwick-Jackson I changed at half-time because he is injured," he said.
"I changed [Juan] Mata to give him rest and also [Anthony] Martial and then Will Keane is injured again. It is unbelievable, but it is also the programme I think."
Manchester United will face the return leg against Danish side Midtjylland on Thursday still very much favourites to progress to the round of 16. Indeed, having seen their top four challenge fade away in the Premier League, winning the Europa League seems their best hope of qualifying for next season's Champions League.