EMIRATES STADIUM, London — It just had to be Diego Costa, didn't it?
Not since 2011 have Arsene Wenger's men defeated Chelsea in the league; it's three years since they last scored a Premier League goal against them, too. That's over nine-and-a-half hours of football.
Costa was booed throughout the game by the home support, especially when he was substituted late on. But he is the villain every Premier League club would love to have. Yes, even Arsenal.
The Spain international comes in for plenty of criticism—some not always justified—yet when he's in the sort of form he finds himself at this moment, his worth to Chelsea can't be denied.
That's six goals in six games under Guus Hiddink now. If Chelsea are to stand any chance of realising their top-four dream this season—one that remains fanciful despite their latest victory over Arsenal—it's Costa who will deliver it.
While the controversy of another Arsenal player being sent off against Chelsea will make the headlines, we shouldn't allow it to detract from Costa's brilliance.
His shenanigans in September when he riled Gabriel Paulista into seeing red were Costa at his worst; his role in Per Mertesacker suffering the same fate this time around was the Chelsea man at his very best.
This wasn't about gamesmanship; it was about world-class forward play.
When Willian broke deep in Chelsea's half, Costa had one thing on his mind and that was to isolate Mertesacker, exposing the acres of space behind the Arsenal back line in the process.
Laurent Koscielny had been marking him, but Costa's looping run to sit on Mertesacker's shoulder was expert. His quick thinking meant that all he needed was for Willian to execute the right sort of pass and he was through.
That happened, leaving the German defender with little option other than to bring down Costa. The contact may have been minimal, but the intent was clear.
Wenger commented after, saying that Costa had got Mertesacker sent off. It was evidently a complaint from the Arsenal boss, but it was equally a back-handed compliment. Of course Costa did, yet this time it was more about his ability as a player that had exposed an Arsenal defender, and not an act of petulance.
Costa took the gamble that Koscielny wouldn't track him, that he would pass him over to his team-mate. That happened, and it proved a poor decision that highlighted the naivety of Arsenal's rearguard.
As we've seen time and again, naivety doesn't win you titles.
The moment Mertesacker lunged in desperation, he gave Costa exactly what he was looking for. And what striker in the Premier League wouldn't accept a gift like that?
That Costa would score the game's lone goal just six minutes after Mertesacker was dismissed only served to rub salt into those gaping Arsenal wounds. The striker wasn't just tormenting the Arsenal players, he was frustrating their fans by being the man to put Chelsea firmly in control.
Those supporters weren't booing Costa because of his perceived antics, either. They were doing it because they're sick of the sight of him.
Costa is becoming the new Didier Drogba. The Ivorian relished facing Arsenal during his prime, scoring 13 goals against them for Chelsea in all competitions.
Drogba was rampant as he terrorised the likes of Thomas Vermaelen and Kolo Toure. There was once even a point when Philippe Senderos was the young hope for Arsenal's future, but facing Drogba arguably ended that notion.
Drogba was Arsenal's bogeyman—the one player who gave the Gunners sleepless nights whenever they faced him. The mere mention of the bogeyman is supposed to convince children to behave better, only the former Chelsea forward brought the worst out of Arsenal's defenders.
After three Premier League matches against them, it's exactly what Costa is doing now. He's scored twice in those clashes, while his performance in September's 2-0 win was a major factor in Chelsea taking three points.
How many times will Wenger suffer at the hands of a Chelsea forward before he does something about it?
When this game was even numbers, Chelsea were already on top because of Costa's presence. He was playing with that edge we should applaud.
The contrast at the other end of the pitch must have been sobering for the Arsenal manager. For all their talent, Theo Walcott and Olivier Giroud offered very little. The France international was sacrificed after Mertesacker's red card, but it's debatable if he would have impacted this game like Costa did.
He doesn't impose himself enough. In the big matches, Giroud makes it easy for defenders and so, too, does Walcott.
Chelsea end sings over and over: "Diego Costa - he's done it again."— Dan Levene (@danlevene) January 24, 2016
With a central defender also lacking pace, Chelsea were rarely exposed on Sunday. They protected John Terry expertly, but then Arsenal didn't do enough to get at the Chelsea captain and ask questions.
Had Costa been wearing red, you can bet he would have. That's his game, and defenders—Arsenal's in particular—really don't like it.
Whether it's begrudgingly or not, Wenger has to admire Costa for everything he has done whenever he has faced his team.
For good or bad, Wenger and the rest of the Premier League's managers know they could all do with a Diego Costa.