The great eras in football tend not to fall to pieces overnight or end in one great Hollywood finale, instead they disintegrate over months and years until one day no-one can quite recall what it was like when they so impregnable and so certain.
Arsenal will still be in fifth place in the Premier League come tomorrow, only five points off the Champions League places but, as so often is the case these days, they find themselves diminished.
Arsène Wenger has only ever lost five North London league derbies but the problem for him is that four of those defeats, including the one at White Hart Lane yesterday, have come in the last four seasons. Slowly, but perceptibly, these two clubs are passing one other in the natural order: it is Spurs who are the more powerful, the more dangerous and it is Arsenal who put up resistance, much of it admirable, but ultimately doomed to failure.
That was the nature of it yesterday, when Wenger's side started the brighter until the big boys took charge towards the end of the first half. Gareth Bale, relatively subdued by his high standards scored the first, then Aaron Lennon, who out-shone Bale, added the second and suddenly we were again examining a range of mishaps familiar to the Arsenal of 2013.
This time it was the defence that was dreadfully out of tune in allowing almost identical balls in behind them from the Spurs' left channel to permit first Bale and then Lennon to run at Wojciech Szczesny and undo much of the good work Arsenal had done up to that point. Szczesny shouted at Thomas Vermaelen, Vermaelen glared at Per Mertesacker and everyone wondered why Nacho Monreal had just stopped tracking Lennon's run for the second.
Each time, the default position of Wenger is to confront his team's mistakes as if they are a new phenomenon but really the same old errors are being perpetrated again and again. He pointed out yesterday that his side had the best defensive record in the league away from home until he was reminded that this was not the first time his side had fallen to two goals in quick succession.
There were echoes of the defeat at home to Manchester City in January when a 10-man Arsenal conceded two around the mid-stage of the first half and never recovered. The defeat to Chelsea at Stamford Bridge in the same month featured two decisive goals for the home side in the first 16 minutes. Reluctantly Wenger agreed. "It happened many times," he said, "and only in the big games".
There is much to admire about Wenger's willingness to face up to the most difficult questions, as he did once again yesterday. But when he earnestly announced "We were not efficient in the zones where it matters: at the front and at the back", you did get that looming feeling that satire could soon be pronounced redundant when it comes to this manager and this club.
Meanwhile, the same old tensions play out on the pitch. Jack Wilshere, the stand-out Arsenal performer again, tried desperately to create some kind of momentum with the anguished aspect of a man who realises he has come of age at the club 10 years too late for the good times. Mertesacker, even in spite of his goal, behaves as if every passing minute is an agony. No-one is capable of taking responsibility.
The decline is incremental. It is not as if Arsenal are bobbing around mid-table, but yesterday was another small descent further into mediocrity. The travelling support rose to the defence of their manager when he was taunted by the Spurs fans but back at the Emirates when they face Reading later this month, you can imagine that the mood will be different if things go awry.
The likelihood of the putative Middle East consortium's takeover of Arsenal reported yesterday is difficult to judge, but the very suggestion of it is one more black crow on Wenger's shoulder. He has fought for Arsenal to be run according to his principles for so long but there is very little he can say about Spurs with an annual wage bill of around £50m less than their Champions League-flush rivals.
And this was Spurs' day. Not, as might have been expected in the past, a heroic one-off in which they reached beyond their everyday capabilities to chisel out a famous win. This time they simply exerted their own superiority over Arsenal.
This Tottenham side has better players, it is more robust and better organised and while there were moments when Arsenal had more of the ball and greater pressure, Andre Villas-Boas' team never looked on the rack.
There was an exceptional performance from his central defensive pairing, especially the Belgium international Jan Vertonghen who was simply superb against the limited Olivier Giroud. So too Michael Dawson on whose future it could be said Villas-Boas got lucky. At the start of the season he was prepared to lose this redoubtable Yorkshireman who has now started the last nine league games.
There was little spark from Arsenal old boy Emmanuel Adebayor, taken off injured in the second half, but he was replaced by Jermain Defoe, back for the first time in a month. Bale was quiet, sticking too rigidly to a central role when he might have had more joy attacking Carl Jenkinson down the left, but he still scored his 20th Spurs goal of the season. Gylfi Sigurdsson, picked ahead of Lewis Holtby, was well worth his place in the team.
Sigurdsson spotted Bale's run for the first goal on 36 minutes of a game that Arsenal had hitherto had the upper hand. Then Scott Parker, another solid performer, broke from the same position on the left to pick out Lennon's run from right to left and the winger took the ball around Szczesny. Pushed into a corner, there is simply not the confidence in this Arsenal team to turn games around.
Mertesacker's header from Theo Walcott's free-kick from the right six minutes after the break flicked off Bale's head on its way in but after that there was precious little. Aaron Ramsey, switched to right-back after Jenkinson went off injured, struck a shot wide, so too did Walcott with a free-kick. The life slowly waned in Arsenal's game, much as it once did with Spurs in these derbies back in a past that feels increasingly distant.