All the teams chasing Arsenal have got things they need to work on - for Chelsea, their lack of discipline is something that has to change if they are going to challenge for the title.
Moises Caicedo's dismissal in Sunday's 1-1 draw against the Gunners was the fourth time in 13 Premier League games that a Chelsea player has been sent off this season.
One of those red cards, for Malo Gusto against Forest, came so late it did not affect the outcome but against Manchester United, Brighton and now Arsenal, they have been a man down for a significant part of each match.