Inside the first 20 minutes, disaster struck for Spurs. Son, one of their key players, had been largely isolated in the early exchanges of the match but attempted to latch onto a ball in behind.
As he began to sprint, he could be seen pulling up and holding the back of his hamstring.
He fell to the floor and clearly knew the writing was on the wall. Moments later, he had been substituted off, with Erik Lamela – who scored a wondergoal before getting sent off – replacing him.
Son’s likely absence will no doubt be a major concern to Mourinho going forwards, and he gave the latest update on the forward after the match.
‘That’s football,’ said Mourinho. ‘I don’t know how long it is.
‘It’s muscular. Muscular is always not easy. He’s a guy who normally recovers very, very well from any kind of injury.
‘That’s football, that’s accumulation of matches. In the Europa League the other day I gave him 30 minutes rest. 90 minus 30 is 60 but 60 is still 60.
‘When you are in so many competitions, some players have more minutes than others, which is normal. It’s something that can happen.’
Fifteen minutes after his introduction, Lamela had scored one of the goals of the season as he banged in an audacious rabona to give Spurs a 1-0 lead.
The lead didn’t last before half-time, with Martin Odegaard sweeping home a Kieran Tierney cross.
Davinson Sanchez was penalised for catching the Arsenal striker after he’d sliced the ball horribly away from goal before tucking it into the bottom corner, with Hugo Lloris diving in the opposite direction.
Things went from bad to worse for Mourinho’s side when Lamela was sent off for a second bookable offence with 15 minutes left to play.
It proved to be decisive as Arsenal beat their London rivals 2-1 on the night.