Manchester United great Rio Ferdinand has dubbed referee Peter Bankes's decision to dismiss Casemiro against Chelsea as 'harsh'.
With the Red Devils 2-0 up and coasting, the Brazilian midfielder was given his marching orders on the brink of half-time for a challenge on Andrey Santos.
While already on a yellow, Casemiro attempted to win the ball off the Blues winger with a sliding challenge from behind. He got the ball but in the process brought down Santos with a tackle deemed worthy of a second yellow by the referee.
Casemiro left the field in disbelief, shaking his head endlessly as he walked towards the tunnel.
The 33-year-old veteran had been booked, a definite yellow card, earlier in the half for a late challenge on Enzo Fernandez in midfield.
Taking to X at half-time, former United centre-half Rio Ferdinand criticised Bankes' dismissal of Casemiro.
He wrote: 'Positive 1st half…. Enjoying seeing us cross the ball - making Chelsea defend… Both goals from crosses..
'Got a 6ft 5 CF - put the ball into him and let him make it uncomfortable for the defenders - flick on for the red card.
'Casemiro - given the referee the option. Harsh but allowed him to even it up. Need to keep being positive 2nd half.'
It had been a chaotic first-half at Old Trafford beginning in the opening exchanges when Robert Sanchez was dismissed.
After Benjamin Sesko won a flick-on, the Spaniard brought down Bryan Mbuemo after the United winger took the ball around him, leaving the referee with little choice but to hand him a straight red.
Maresca then made a host of early changes, with Pedro Neto and Estevao taken off for Filip Jorgensen and Tosin Adarabioyo within the ten minute mark.
The Blues then suffered a huge blow as Cole Palmer was withdrawn early on with what looked like an injury.
United went on to put themselves two goals in the lead before Casemiro's dismissal in a game so crucial for Ruben Amorim.
Bruno Fernandes scored the first with a close-range effort on a soaking wet day in Manchester, before Casemiro headed home the second.