The two stars face off on Sunday, but have played against each other a long time ago.
Chelsea lead from Arsenal in the Premier League table by 10 points. Victory would surely see them claim the title for the first time since Jose Mourinho returned to the club.
There will be several big battles in the game, but perhaps how Chelsea plan to shackle Alexis Sanchez could be the real key to success.
It could be that Mourinho employs his workhorse winger Willian to the job on the Chilean, who scored the two goals at Wembley last weekend that took Arsenal to the FA Cup final.
If he did, it would not be the first time these two went toe-to-toe. In fact, they first faced each other many years ago.
The attached picture shows Alexis and Willian battling for the ball in a South American under-20 Championship game back in 2007.
It was a game that Chile lost 2-0 when Willian and Alexis would have been just 18-years-old.
Now, eight years down the line, the pair will face off again in an entirely more grown-up battle.