The match was briefly halted after Williams drew attention to alleged racist sounds coming from the Estadio Civitas Metropolitano crowd.
At half-time, Aston Villa thought they had one foot in the Champions League. But by the end of a chaotic game against Chelsea, the Midlands club were relieved to take just another point towards a top-four place.
Things have gone off the boil for Ten Hag at Old Trafford.