Gunners destined to end quest for title the hard way
There are two certainties in life when Diego Costa races on to a through-ball and Per Mertesacker rumbles over to intercept. One is that the Arsenal captain will arrive too late and the other is that Chelsea's centre-forward will turn his tumble into performance art.
If only the rest of life were so predictable. Arsenal fans would certainly like this title race to be more unsurprising. But there is no release from the funfair ride that sees the Gunners locked together on points 44 with Manchester City - three behind Leicester, who were meant to have crashed out of the top four places by now.
Instead, Leicester wallop Stoke 3-0, City contrive a point at West Ham and Arsenal extend their run of league games without a victory over Chelsea to nine after Mertesacker is sent off on 18 minutes for a needless foul on Costa.
It was a foul, however much Costa made of it. A red card too, since the none-too speedy Mertesacker was denying a clear goal-scoring opportunity.
In that situation, you would expect a World Cup winning centre-back to run the risk of conceding the goal in favour of keeping 11 men on the pitch (especially as Arsenal can always be fancied to score at home).
Instead, the captain took a gamble that doomed his team to playing with 10 for 72 minutes against a side who looked like Chelsea again and not London's most ragged Premier League club.
These so-called 'turning points' in a 38-game campaign often turn out to be nothing of the sort. You could just as easily pick out five decisive moments when things went right.
Arsenal, however, leave us no choice but to conclude they never do anything the easy way - as they showed by conceding a last minute equaliser at Liverpool; or, as they did in their Champions League group, losing their first two games - to Dinamo Zagreb and Olympiacos - but somehow still progressing to a round of 16 tie against Barcelona.
A talent for melodrama shaded into comedy when Arsene Wenger reacted to Mertesacker's dismissal by withdrawing Olivier Giroud, the centre-forward, in favour of Gabriel, a centre-back.
That change, though baffling to Giroud, who stared at the floor for what seemed an eternity before shuffling off, was not by itself an error. As Wenger explained later, Arsenal needed "speed" to play on the counter-attack and Giroud is not that kind of soldier.
Equally Gabriel's rushed introduction turned out to be calamitous. Almost his first act was to be slow to spot the danger in a Branislav Ivanovic cross to Arsenal's near post. In came Costa again, to turn the ball past Petr Cech.
From there on, Gabriel was a sack of nerves, while Costa made room in his special scrapbook of momentous theatricality. The cause of a red card and the game's only goalscorer: Costa is a much more convincing presence when he turns away from feuds.
So Wenger's great quest to reclaim the championship 12 years after it last finished up in Highbury and Islington is showing signs of strain, but not terminally so.
Two points from a possible nine against Liverpool, Stoke and Chelsea is underwhelming. But the performance level is not plunging.
The 3-3 draw at Anfield was a barnburner, with a classic late Liverpool equaliser, and a 0-0 draw at Stoke would have been happily filed away back in the days when Arsenal tended to shatter in the Potteries.
This time they can ascribe a defeat to Mertesacker's misjudgement, even though Wenger was itching to blame Costa for simulation, and to the curse that hangs over them in this London derby.
Arsenal have not scored against Chelsea in the league for nine and a half hours. Their attempts to break that run were not helped by Mathieu Flamini charging into the Chelsea penalty box to indulge an apparent lifelong dream to play centre-forward.
Three times Flamini made a hash of meeting balls into that area. It was a mystery that his team-mates - or Wenger - failed to tell him to keep the hell away from the six-yard box.
Finishing duties ought to have fallen to Theo Walcott, who had an off day, or Aaron Ramsey, or Alexis Sanchez, who returned from injury, along with Mesut Ozil.
The good news for Arsenal is that their aberrations are no longer borne of flimsiness, or frailty.