With Manchester City's relentless pounding of all in their path and Liverpool rocking along at four goals a game recently, tonight's meeting of London elites might still be definitive but not in the way we anticipated the last time Arsenal and Chelsea kicked a Premier League ball.
Jose Mourinho cast this fixture as the match everyone wanted to see, first against second in one of the great European leagues. That was nine days ago. City have subsequently augmented the six-goal immolation of Arsenal by easing into the Capital One Cup semi-finals by way of Leicester and smashing another four goals on the road at Fulham.
Chelsea's laboured home win against Crystal Palace, which prompted Mourinho's heightened assumptions about the significance of tonight's trip to Arsenal were further undermined by the calamitous Capital One Cup exit at Sunderland. Yes, a victory tonight would see Chelsea draw alongside Liverpool at the top or take Arsenal back into the outright lead. But both sides enter the fixture clouded by doubts about their capacity to keep pace with Merseyside and Manchester, never mind set it.
The ever-shifting dynamic at the top is arguably more of a concern for Arsène Wenger.
Suddenly, after three games without a win, two of those in the Premier League, Wenger can almost feel the ground shifting uneasily beneath his feet. Defeat tonight will leave Arsenal in fourth spot, not the landscape he surveyed on the last day of November when his team swept imperiously through Cardiff.
In that urbane way of his, Wenger understands the doubts. "At the moment everybody still questions us, even more after our defeat at City," he said.
"We haven't won it for a long time. That's why they question us. It makes the challenge more interesting. It adds pressure but you cannot play in the Premier League without pressure."
Wenger's belief in the football values he espouses is absolute, as is his optimism, which depending on outcomes, can appear myopic. Hence the positive spin he put on the 6-3 defeat at City. That result, when coupled with the defeat at Old Trafford, suggests Arsenal have a problem winning the big encounters.
"People are only keeping in their mind the big matches that we lose. We have won some big games," is his answer for this.
"What is at stake is if you want to win the Premier League, you want to win the big games at home. It's as simple as that.
"We can have even more belief after the game at City. Despite the fact we conceded goals it was not all negative because we could have scored six as well.
"I believe that we have come out of that game even stronger in our belief, even stronger in our resolute attitude, because we have shown that we can be very strong defensively, and on the day we have shown that we can be dangerous against anybody. We have to show that against Chelsea."