When Manchester United's Wayne Rooney earned a straight red card for his professional foul on West Ham's Stewart Downing at the end of September, leaving him with a three-match ban, it provided the rare opportunity Juan Mata had been patently waiting for.
The Spain international now had the chance to show that he deserved to be starting ahead of the suspended Rooney, after the arrival of Radamel Falcao had relegated him to the substitutes' bench.
But unfortunately for the 26-year-old playmaker, he has done nothing over the past few weeks to convince United boss Louis van Gaal that he deserves to keep his place in the starting line-up for this weekend's visit to Premier League champions Manchester City.
Mourinho's reasons for selling Mata become clear
Watching Mata against Chelsea on Sunday, it became apparent why Jose Mourinho allowed the Spaniard to join the Red Devils for £37.1 million in January.
At the time it looked an inexplicable decision by the Portuguese coach. Mata, after all, had been voted as Chelsea's Player of the Season for two years running and had been one of the Premier League's most outstanding performers since completing his move to Stamford Bridge from Valencia in 2011.
- Mourinho says Juan Mata is not a special player
- Video: Mata has the best first touch in the EPL
- Atletico Madrid keen to sign Mata in January
And Mourinho wasn't selling Mata to an overseas club; he was selling him to Manchester United - a direct rival.
But Mourinho was never convinced by Mata, who he felt lacked the physicality, stamina and work ethic to become an integral member of his squad.
Mata may have excelled under Rafael Benitez, but Mourinho isn't Rafael Benitez - his teams do not rely on individuality, but become a formidable machine by working as a unit, with every player carrying out specific duties across the pitch.
"For me Juan is a very good player and I look at him as a very good player. I don't look at him as a special player because of certain circumstances." - Mourinho on Mata.
Mata was a passenger against Chelsea
There are no room for passengers in a Jose Mourinho team - and that's precisely what Mata, who picks up £140,000-a-week, was for Manchester United against Chelsea on Sunday.
This was his chance not only to convince Van Gaal to stick by him ahead of the Red Devils' biggest match of the season so far this weekend, but also to get one over on Mourinho and the club that sold him, despite his heroics, earlier this year.
But, just as he did against Everton and West Brom, the Spaniard flattered to deceive - and was eventually subbed off with 25 minutes remaining for Manchester United's 18-year-old striker James Wilson.
Mata struggling at United
Because of his physique, Mata sometimes struggles to get himself around the big Old Trafford pitch and lacks the same breathtaking pace of some of his teammates. This can often hinder United when they launch one of their trademark counter-attacks.
If Angel di Maria, Wayne Rooney, Antonio Valencia or even Adnan Januzaj are the men who lead the break, then United stand an excellent chance of getting from one end of the pitch to the other in the blink of an eye. Mata, on the other hand, slows the play down.
The former Chelsea star is at his most dangerous just outside the penalty box. That left foot of his is capable of wreaking havoc, and his technical qualities are superb. But Rooney is certainly the more complete package and will walk back into United's starting line-up for the trip to the Etihad Stadium.
Rooney a better option for United
United's captain might not be blessed with the physique of what you might describe as an athlete - but he is blessed with deceptive pace, and was even clocked as Manchester United's fastest player in September's 4-0 win over Queens Park Rangers, ahead of Di Maria, with a top speed of 20.3mph.
Unlike Mata, Rooney also has the build to put himself about for the team. The England skipper is capable of dropping back into central midfield and putting in a shift, better than the lightweight Mata is.
Gary Neville called it
Former Manchester United captain Gary Neville said before Mata signed in January that he doubted whether the left-footed playmaker would fit the Red Devils' philosophy.
"Does he fit with what I would call the typical philosophy of Manchester United? I would say no," the England coach said on Monday Night Football. "What it could be is the start of something to lead to other things, but typically I wouldn't say he fits."
And so it's proved. Mata, after failing to take his chance over these past few weeks, can expect to find himself back on the subs' bench now that Rooney's back.
What happened to Mata under Mourinho at Stamford Bridge will happen to him again under Van Gaal at Old Trafford.