Scott McTominay had Red Devils out in front early on, but Diogo Jota found a response for the home side, sending the match into half-time on level terms.
Young picked up a first booking just seven minutes after the restart, and it didn't take Dean long to give him his marching orders.
A sliding challenge on Jota from the right-back as he tried to recover a sloppy back-pass was adjudged to be worthy of a second booking just minutes later, and the England international was sent for an early bath.
The sending-off made Dean the first official in Premier League history to bring up a century of red cards.
It was the tenth red card of the season issued by Dean in just 24 matches, the most in the league by nearly double over Michael Oliver's six.
Dean is also nearly double his nearest competitor in the all-time race, with no other official having even reached 60 red cards in the top flight for their careers.
The 50-year-old first broke into the top flight for the 2000-2001 season and his career has seen its share of highs and lows, including a demotion to the Championship for a weekend in 2017 after a string of controversial decisions, including choosing to send off Ross Barkely during the Merseyside Derby.
100 - Following Ashley Young's dismissal, Mike Dean has now handed out 100 red cards in the Premier League, the most by a referee in the competition's history. Ton. pic.twitter.com/p5L3F3kRdR— OptaJoe (@OptaJoe) April 2, 2019
Other low-lights include mouthing "off you pop" after sending off Brighton defender Lewis Dunk at the Vitality Stadium in December as well as handing a second yellow card to the wrong Brighton player.
Supporters of Arsenal launched a petition in 2015 to have Dean banned from officiating their matches after an incident against Chelsea involving Gabriel and Diego Costa that saw the Gunners man sent off. In that case the FA rescinded the red card and issued a suspension to Costa for violent conduct.
He faced a similar set of complaints in January 2017 for handing West Ham's Sofiane Feghouli a straight red after a challenge with Manchester United's Phil Jones.
The incident left Jones on the pitch injured, though replays suggested that it was in fact Jones who make the reckless challenge.