BBC pundit Garth Crooks has revisited Chelsea's decision to sell Petr Cech to Arsenal, branding it 'borderline unthinkable'.
Cech was impressive as Arsenal beat Sunderland at The Emirates, making a key first half save from Fabio Borini.
The Gunners are in second place with 30 points, while Chelsea have had a spectacular regression this season, in 14th place with 15 points.
Crooks said: "If Arsenal do happen to lift the Premier League title, it will be partly down to the awful performances of some of the best teams in the country and partly down to the brilliance of Petr Cech.
"That Jose Mourinho sold Cech to his arch rivals is one thing, but then consider that Mourinho sold Cech to his nemesis Arsene Wenger, who might go on and win the title with Mourinho's once prized possession. It is bordering on the unthinkable."
The kindest thing you could say about Jose Mourinho here, would be to point out he did not want to sell Cech to Arsenal.
The Guardian reported in the summer that Mourinho was set against selling to Arsenal, and made his feelings known to owner Roman Abramovich, who overrruled him.
Looking back this could have been the very moment it all went sour at Chelsea, while for Arsenal the door is open to win the league with no team looking consistent so far, it is just a question of whether they can negotiate their numerous injuries and actually do so.