The 9-0 loss at Old Trafford tied the record for the heaviest loss in Premier League history.
One of Southampton's two red cards in its 9-0 loss to Manchester United in the Premier League was overturned on Thursday.
Jan Bednarek was adjudged to have brought down Anthony Martial in the penalty area in the 86th minute of Tuesday's match and was sent off for denying an obvious scoring opportunity.
Martial appeared to be already falling before making the slightest of contact with the Poland center back, and Southampton appealed against the decision.
The Football Association said the appeal was upheld by an independent regulatory commission and the red card had been rescinded.
Bednarek will now be available for Southampton's away match against Newcastle on Saturday.
The 9-0 loss at Old Trafford tied the record for the heaviest loss in Premier League history. Southampton already shared that record after losing by the same score at home to Leicester last season.
Alexandre Jankewitz was also red-carded for Southampton on Tuesday, after just 82 seconds.
