LONDON -- In fairness to Maurizio Sarri, the Chelsea manager had done well to stave off what appeared to be the inevitable when he succeeded Antonio Conte at Stamford Bridge during the summer. Until Saturday.
Nobody doubted Sarri's tactical nous and devotion to a high-intensity, attack-minded style of play, but the big question was whether he could force square pegs through round holes to make it work in the Premier League.
Could he really transform a squad of players signed by Jose Mourinho and Conte and turn them into a team as exciting and as effective as the Napoli outfit he left behind to take charge at Chelsea?
The answer has been an emphatic "yes," but as Tottenham left the Wembley pitch celebrating a 3-1 victory over their London rivals, there was the sense that the wheels are beginning to wobble on the Sarri bandwagon.
This was Chelsea's first competitive defeat of the season, in their 19th games across three competitions under the new coach, so it would be wrong to suggest they have been found out. But the fine start that brought wins in their first five league games has since subsided into a more unimpressive run.
Chelsea have won just two of their past six games, with the first defeat of the campaign coming against Spurs. While they remain in the top four, they are seven points behind leaders Manchester City, and that gap is only likely to increase, such is the formidable form of Pep Guardiola's reigning champions.
Perhaps more significant is the four-point lead over fifth-placed Arsenal, who can move to within one point with a win at Bournemouth on Sunday; Chelsea's priority this season is a return to the Champions League rather than a tilt at the title.
Holding off Arsenal -- and Manchester United if they ever find some form -- will be the measure of success for Chelsea this season, but the defeat against Spurs was enough to set some alarm bells ringing. After this reality check, Sarri knows he must find a way to re-ignite his side's winning streak.
"I am disappointed because we played very badly," Sarri said. "I think we played very badly in all directions; physically, mentally, technically and tactically. We have to try to do something because the defensive phase was a disaster today.
"The offensive players pressed badly, the midfield defended not very well, and the defensive line was a disaster," he continued. "I knew we had some problems, and with this performance today, it was clear to everybody that we have problems to solve."
The first issue to address is Chelsea's predictability factor; Sarri is rigidly loyal to his 4-3-3 formation, so much so that he does not even tweak things when his team are chasing games. He has ripped up the three-man defence that suited the players left behind by Conte, but when faced with a team as potent as Spurs, the back four looked worryingly vulnerable.
David Luiz has never been convincing in a four-man alignment, and he was awful against Spurs, with two of the home team's goals down to the Brazilian international's questionable defending. When Luiz struggles, it negatively affects those around him. Antonio Rudiger was also all over the place at Wembley.
Moreover, when Jorginho attempted to stop Son Heung-Min from scoring Tottenham's third early in the second half, it was a result of Luiz making another mistake in his initial attempt to stop the South Korean forward.
Overall, Jorginho was left to put out too many fires as Spurs swarmed around him from all directions. The Chelsea midfielder was looking over his shoulder at Luiz and Rudiger due to Harry Kane's dominance but also had to cope with Christian Eriksen and Dele Alli. It was too much.
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Sarri's determination to accommodate Jorginho and N'Golo Kante in the same midfield makes sense because they both are world-class players. However, by giving Kante more licence to get forward, he is denying Chelsea the qualities of their best defensive midfielder.
No other player sniffs out danger quite like the 27-year-old, who is arguably the best defensive midfielder on the planet. At times under Sarri, though, Kante plays as far forward as a No. 10; against the quality of a team like Spurs, it left Chelsea too open and contributed to the continuation of a trait that has seen them fall short against the league's top clubs.
Aside from a 3-2 home win against Arsenal on the second weekend of the season, when Unai Emery was still grappling with his new Gunners squad, Chelsea have been unable to beat any of their big-six rivals. Home draws with Liverpool and Man United have been followed by an away defeat vs. Spurs, and the inability to control midfield in all of those games has been key.
Chelsea, who host Man City in two weeks' time, also sustained their unbeaten run despite neither Alvaro Morata nor Olivier Giroud being good enough to provide 20 goals a season up front -- how they miss Didier Drogba, who retired this week, and Diego Costa, a scorer for Atletico Madrid vs. Barcelona on Saturday -- but the cracks are beginning to show.
Sarri needs to find a Plan B for when things are going wrong, as they did against Spurs, who effectively sealed victory with two goals in the game's opening 16 minutes. Having answered some of the early question asked of him in positive fashion, now he faces more.
Namely, is he flexible enough to go negative? And, does he have the players to make those alterations? Despite the many positives there have been since he took over, not enough has been seen to suggest the answer to either of those questions is "yes."