Liverpool youth player Oakley Cannonnier, 14, helped the Reds overcome Barcelona in the Champions League, feeding the ball quickly to Trent Alexander-Arnold to set up Divock Origi’s late winner.
His smart-thinking in the 4-0 win at Anfield came after the ball boys were given a video presentation on how they could help Jurgen Klopp‘s team.
The Liverpool boss had noticed how much Barcelona’s players had argued or contested every decision in the first leg, with balls boys later told to return balls to the Reds quickly.
Mourinho has praised the club’s meticulous planning, telling RT: ‘You want a quick throw-in, the ball boy needs to know that you want a quick throw-in. The ball needs to arrive fast.
‘The goalkicks, the tempo of the game, the ball boys can also play a part in a good structure.’
He added: ‘In this game, the kid, very intelligent, very bright.’
Mourinho ditched regular ball boys during his own spell at United, replacing them with academy players in 2017.
Matchday ball boys and girls had been chosen by the Manchester United Foundation before Mourinho opted to replace them with youngsters with ‘more knowledge of football.’
And after Liverpool outwitted Barcelona to reach their second consecutive Champions League final, Mourinho seemed to have another dig at United, who sacked him back in December.
‘I had a club where they never understood how important the ball boys are,’ he added.
‘I was a ball boy, a top ball boy… when I was a ball boy, I even knew where the players wanted the ball for a corner, so they didn’t need to touch the ball.
‘(At) a real football club, every detail is very, very important.’