Game, set and match in one moment decided the game
One of the reasons Diego Costa doesn't fit in too well within the Spanish national team system is his preference for a more direct style of football.
Quick ball is what he wants to run onto and part of his problem earlier in the season was the fact that he had stopped making the type of movements that Cesc Fabregas in particular could spot for through balls.
Ex-Ireland full-back Paddy Mulligan had described that reluctance to make runs as an "awful habit" after watching a performance he put in against Norwich in late November.
Ever since Jose Mourinho was cast aside as manager though, Costa seems to have found his mojo again.
That should have been a warning to Arsenal, who do like to play the type of high line that suits the passing football they prefer.
Their line may not be as aggressive as it once was in a bygone era, but with Per Mertesacker marshalling the defence, there is always an element of danger, given that he has the turning circle of an oil tanker.
Against Tottenham back in early November, Arsenal's backline was caught out by a ball over the top into the space behind Mertesacker as Harry Kane latched onto a long pass from Danny Rose and finished it off:
That time, Koscielny was also culpable for pushing up to play offside and Mertesacker avoided a red card - unlike Sunday night - since he never caught up with Kane.
Given that Chelsea started with the block of John Obi Mikel and Nemanja Matic in front of the defence, it was clear that Guus Hiddink was not intending to play through Arsenal, hence making a direct ball over the top a present danger.
It is the way Chelsea tend to play when they face Arsenal, knowing they can profit on the counter.
Once Costa got in behind and Mertesacker moved to challenge, there was only going to be one result: a red card and an uphill challenge for the Gunners.
The converse lesson for Mertesacker is the case of Chelsea captain John Terry, who is similarly lacking in pace but more adept positionally.
During Andre Villas-Boas' tenure, the ex-England defender suffered in a high-line, famously being troubled throughout a 5-3 loss to Arsenal at Stamford Bridge in 2011.
Since then, he has thrived in a deeper position with protection around him, bar the odd blip in form.
For a big game like this against a direct opponent, sitting the defensive four further back and pulling a midfielder slightly further back, to shadow Chelsea's more creative players in the space between defence and the engine room, could have prevented the chance that Costa had to run in behind Arsenal's BFG.