The captain played his part in an encouraging start for United, which saw us take a 2-0 lead at the Estadio Dragao. But the home side fought their way back into the contest, and after they went ahead early in the second half, Fernandes was dismissed for a second bookable offence in the final 10 minutes in his homeland.
Fernandes had attempted to connect with an enticing Alejandro Garnacho cross, but was instead adjudged to have caught an opposition defender with a high boot.
Porto looked to set to hold on for all three points, but United were able to rescue a point late on, thanks to a stoppage-time header from substitute Harry Maguire.