United's hopes of finishing in the Premier League top four suffered a potentially fatal blow as Nuno Tavares
Bukayo Saka penalty and Granit Xhaka's 25-yard strike sealed victory with United only able to muster a Cristiano Ronaldo effort in response.
Had United scored, they would have levelled the match at 2-2 after a spell in which they were the better team but Fernandes rolled his effort against the post.