Arsenal have produced awesome football this season to lead the Premier League table for most of the campaign.
Yet, defeat at home to Chelsea tonight and they will drop to fourth! Showing how tight and tough it is at the top.
Fresh from being thumped 6-3 at Manchester City, when the referee announced game, set and match at the end rather than blow his whistle, if the Gunners lose again, they will face some serious questions about their title credentials.
And with justification because, having also been defeated by Manchester United this term, the Gunners would stand accused of lacking a champion mentality when the crunch comes.
You can't accuse the current Chelsea players of that. Most of the boys in blue have won trophies at home and abroad and are hungry to add more medals to their impressive collections.
While the likes of Aaron Ramsey, Mesut Ozil and Olivier Giroud have received lavish praise in recent months, Chelsea have faced criticism for the inconsistency of their strikers.
Due to his sparing use of Juan Mata and some distinctly poor displays, Mourinho has not enjoyed the love in he had with the English press in his first spell in charge of Chelsea.
Back then he was full of jokes and jibes, forever sending out the vibe that his side would do the business.
The Special One has become more like the Serious One since returning to west London. It's evident he's not content with his squad and with old reliables like John Terry and Frank Lampard not getting any younger, Mourinho wants to bring in new recruits, if not in January then in the summer, though we all know what Roman Abramovich is like so there are no guarantees how long Jose will be around.
Mourinho insists he'll be at the Bridge for years to come, but Chelsea's Russian owner is so ruthless he makes Cardiff's Vincent Tan look as warm and fuzzy as Santa!
The bottom line is Jose has to keep winning and do it in a style that is easy on Roman's eye, preferably much in the same way that Arsenal have been delivering for most of this campaign.
Tonight the midfield battle will be key with Santi Cazorla, Ramsey and Ozil, who Mourinho managed at Real Madrid, up against Lampard, Oscar and Eden Hazard.
Given that Mata has scored in each of his four starts for Chelsea against Arsenal, it would be wise to play him too.
Mourinho has never lost to Wenger in NINE games. The perfect 10 for Arsene would be a home victory taking the Gunners back above Liverpool and City to the top of the table in time for Christmas, while Jose will be desperate to maintain his unbeaten record against the Frenchman he once labelled a "voyeur" for talking about Chelsea.
Well, we'll all be watching tonight what promises to be a compelling contest, the type of match which could see Mourinho's Chelsea finally catch fire second time around.