Marouane Fellaini was sent off for headbutting Sergio Aguero as a disappointing Manchester derby ended goalless at Etihad Stadium.
Six minutes from time United midfielder Fellaini – who had just been booked for fouling Aguero – was given a straight red card for his headbutt on the City forward.
Aguero had earlier hit the outside of the post before David de Gea saved well to deny the Argentine, as well as keeping out Aleksandar Kolarov.
Ander Herrera headed wide for United while City’s Gabriel Jesus had a late effort disallowed for offside, reports the BBC.
City, who lost keeper Claudio Bravo to injury, stay fourth while United remain outside a Champions League spot in fifth.
United, who are two points behind third-placed Liverpool with one game in hand, are unbeaten in 24 league games but two of their remaining five matches are away to Arsenal on 7 May and Tottenham on 14 May.
City, who face a trophy-less first season under manager Pep Guardiola, are one point behind Liverpool with a game in hand over the Reds.