Chelsea's unbeaten start to life under Maurizio Sarri had supporters dreaming of a title challenge. Saturday's meeting with Tottenham was the long overdue wake-up call, with the Blues slumping to a 3-1 loss to their most hated rivals.
Make no mistake about it: this result had been coming. Chelsea have struggled to control games ranging from Bournemouth and Derby County at home, to BATE away in the Europa League.
Sarri, to his credit, had repeatedly played down his side's hopes of challenging for the Premier League title in his first season at Stamford Bridge. He knew that returning his side to the top-four was the more realistic goal, quite rightly pointing out that Chelsea had problems up front and at the back, with several defenders struggling to meet his demands.
Sarri said the Blues weren't yet at the same level as Manchester City and Liverpool, and that was made painfully clear at Wembley, with goals from Dele Alli, Harry Kane and Son Hueng Min allowing Spurs to move above their visitors and into third place in the table.
As it stands, Chelsea are now seven points behind leaders City, and five adrift of Liverpool. All of a sudden, Chelsea are looking nervously over their shoulders at fifth-placed Arsenal, who are just four points behind and with a game in hand.
There is no need for panic, of course, but this was a chastening defeat for Chelsea. Granted, Eden Hazard was denied a stonewall penalty in the first half, after a foul by Juan Foyth, but the scoreline offered a fair reflection of Tottenham's total dominance of the game.
The Blues had plenty of possession but did very little with it. Indeed, Spurs would have scored far more than three goals had Kane and Son been more clinical, with several clear-cut opportunities squandered.
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David Luiz was particularly poor for two of the goals, failing to block Kane's long-range shot, which was well-struck but shouldn't have found its way passed a very busy Kepa Arrizabalaga. The Brazilian was then far too easily fooled by Son as the Korean breezed past him to make it 3-0 to Tottenham.
Like the rest of his defence, and indeed midfield in front of him, Luiz was bullied by a team playing at a much higher intensity right from the first whistle, as Chelsea made yet another sluggish start.
Still, it wasn't just a question of attitude. There were obvious tactical issues here too, as playmaker Jorginho was successfully man-marked for the second game in a row, this time by Alli.
In his last Premier League match, against Everton, injured Gylfi Sigurdsson with a nasty tackle that was born of frustration. He was just as irritable at Wembley.
He completed fewer passes (43) in any of his previous Premier League outings, so it came as little surprise to see hacking down both Kane and Alli, with the second of those fouls arguably worthy of a straight red card.
N'Golo Kante, meanwhile, again looked uncomfortable in his new role on the right, provoking further questions over his suitability to a more advanced role.
Olivier Giroud added a consolation goal late on and perhaps it could have been a different game had the Frenchman replaced the anonymous Alvaro Morata earlier on but, in truth, Chelsea were outplayed from start to finish.
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Chelsea's over-reliance on Hazard remains a huge concern, particularly as the Belgian has now gone nine games for club and country without a goal.
This was a collective failure, though. Chelsea didn't close Tottenham down well at all, seemingly caught between a desire to press and remain alert to long balls in behind a slow and static defence.
All in all, Sarri has plenty to work on, but then, he knew that already. He has been preaching patience for weeks now, particularly as a run of 12 games in 40 days was always going to put a strain on a side still adjusting to their new coach's demanding style of play.
After his stinging defeat, though, the onus will now be on him to prove his worth both a motivator, as well as a tactician.
Tottenham have now won back-to-back against Chelsea for the first time since 1987 but they have also delivered the obvious but nonetheless painful message to their London rivals that Sarri was right all along: this Blues side should not yet be considered title challengers.