One year after Antonio Conte vowed he would not have a Mourinho season, the United boss has had the last laugh. Well, sort of.
The Italian's last game as Chelsea boss was the FA Cup final win against United and he returns to his homeland with a Premier League winner's medal in his back pocket.
But it was Mourinho who nearly derailed Conte's final season at the helm when their very public spat reached boiling point in the New Year. Just six wins would follow in Chelsea's next 20 games in all competitions before they finally rallied.
And while the pair buried the hatchet in Mourinho's office at Old Trafford back in March, the United boss was not about to start showering him with compliments.
"They only played long balls to [Olivier] Giroud to flick and then Hazard to get second balls in individual actions, and when you play against a team so predictable is quite easy to adapt to it," he told reporters after the FA Cup final.
The irony being that Mourinho bemoaned the absence of both Marouane Fellaini and Romelu Lukaku to give his side a focal point up front. The kind of tactic that is anathema to Conte's successor-in-waiting, Maurizio Sarri.
"If I saw my team defending and counter-attacking after 30 minutes I would get up and return to the bank because I would not be having fun," the former Napoli boss said back in 2016.
Remarkably, just as Conte never came up against Mourinho before he rocked up at Stamford Bridge, Sarri has never had the pleasure, either.
Aside from both managers not having playing careers of note, they share few similarities despite their fiery personalities in the dugout.
Mourinho is the son of a professional footballer who has won 25 trophies to date and got his first break in management with Benfica in 2000 following an apprenticeship under both Sir Bobby Robson and Louis van Gaal.
Sarri, the son of a construction worker, was still working as a middle-aged banker by the time Mourinho made his first steps into management - and is yet to lift a single trophy following spells at nine Italian clubs.
When Mourinho was winning a historic treble with Inter Milan in 2010, Sarri was managing Grosseto in Serie B yet the 59-year-old is now widely recognised as one of the game's great philosophers.
One Pep Guardiola claimed that Sarri's Napoli were 'maybe the best team' he had ever faced. Fernandinho added they played the best football in Europe.
Those quick passing triangles, the way Napoli dominate possession, the marauding full-backs, how they press and counter press at speed, Jorginho pulling the strings, the well-drilled, compact defence...
Can that translate to the Premier League - particularly when Sarri is bizarrely set to take charge at Chelsea days after Conte got pre-season training underway at Cobham?
The argument, as far as the Chelsea are concerned, is that the first week of pre-season is cardio-focused and it is not until the players go on tour that they really start to get to grips with tactics.
When it comes to potential outgoings, too, Willian, has put off any talk about his future until after the World Cup.
Whatever happens, Sarri's arrival presents a new challenge for Mourinho after coming up against Guardiola, Mauricio Pochettino and Jurgen Klopp in recent years.
October 20 will have a large 'X' beside it in his leather bound diary when he returns to Stamford Bridge for his first ever clash with the Italian. Expect fireworks.