The draw keeps the race for Champions League qualification wide open.
Fellaini might have been about to receive a second booking anyway for fouling Aguero when he went head to head with City's striker and aimed a butt in the 83rd minute, earning a straight red card.
City sent on fit-again striker Gabriel Jesus in an attempt to score a late goal and the striker had a stoppage-time headed goal disallowed for offside in a tense finish at Etihad Stadium.
