Manchester City manager Pep Guardiola knew this day would come but it was painful nonetheless - especially as his previously flawless Premier League side were so completely outplayed by Spurs.
Guardiola's run of six straight league wins at the start of his reign ended with a warm embrace for his victorious counterpart Mauricio Pochettino, the Catalan's smile and low-key touchline body language confirming he had no complaints about this 2-0 defeat.
He was as dignified in defeat as he has been in victory - but what lessons emerged from this reality check for the team installed as firm Premier League title favourites?
Spurs defeat a sign of things to come?
Guardiola likes his side to get their opponents on what Sir Alex Ferguson called "the carousel" - a label plucked from the days when Xavi and Andres Iniesta tormented teams by passing as if they were born in possession of a football, and illustrated by two emphatic Champions League final losses for Manchester United at the hands of his Barcelona team.
What happens when a team not only refuses to jump aboard the carousel, but takes decisive action to stop it before it makes its first spin?
Celtic and their manager Brendan Rodgers started it in that 3-3 Champions League classic at Parkhead on Wednesday when they pressed, hassled and harried City relentlessly, never giving Guardiola's players a moment's peace as they were forced to come from behind three times to take a point.
Spurs, with players of a higher calibre, rattled City from the first whistle, with the outstanding Son Heung-min leading the charge while Guardiola's full-backs Pablo Zabaleta and Aleksandar Kolarov were attacked mercilessly. The latter was so unnerved, he slashed Danny Rose's cross into his own net for the first goal after nine minutes.
Only John Stones retained a modicum of composure as Tottenham, following Celtic's example, tore into City. One observer suggested the pace of the first half was so high you needed to be at peak fitness to watch it, let alone play in it.
And on the touchline was the grand orchestrator Pochettino, waving his players forward with demands to press City higher and higher up the pitch. At one point his orders took him into Guardiola's technical area, such was his desire for Spurs to carry out his game plan.
City just went back and back, rattling all the way, as Spurs gave them a thorough going over without demonstrating any of the frailties that allowed them back in against Celtic.
|Not all bad news for Pep...|
|Striker Sergio Aguero had seven shots on goal against Tottenham, four of which were on target, and hit the crossbar. He only had four in total at Swansea last week when he scored twice|
|The visitors had 12 shots in total at White Hart Lane - one fewer than Spurs - and had 58% possession throughout the match|
|City have 18 points from their first seven games this season. Last year they had 15 and were a point behind Manchester United. Eventual champions Leicester had 12|
|After the international break, City have back-to-back home games against Everton and Southampton|
Guardiola will know there will be more where this came from. The Premier League is an unforgiving arena - any perceived weaknesses are pounced upon and highlighted.
He will have learned from this thunderous 90 minutes, and will at least be comforted by the knowledge that not too many teams will have the speed, fitness levels and ability to carry it off for 90 minutes.
As Guardiola rightly said afterwards: "Losing is part of the game. I never thought that we would not lose a game. You can't imagine that. It is normal to the process. Sometimes it happens and it can help us improve.
"It is October. You cannot imagine my team is already done. I am new here. So far it has been an amazing performance but we need more. We have to work more."
Best to learn the lesson early, perhaps.
Bravo still finding his feet
Claudio Bravo is a central plank in Guardiola's future plans for Manchester City but still looks desperately ill-at-ease when placed under the sort of pressure Spurs applied.
Taunted almost every time the ball landed at his feet as Spurs fans revelled in the high-octane approach of their team, he became a symbol of City's struggles, despite a fine second-half penalty save from Erik Lamela.
The 33-year-old was brought from Barcelona after Joe Hart was shown the door, to not only be a goalkeeper but act as instigator of City's style to play out from the back. This day will not be considered a success.
Bravo's interventions arguably led to more attacking opportunities for Spurs than City, firing one clearance high into the danger area and almost getting caught in possession in the early moments of the second half.
It is proving to be a tough transition for the Chilean, with trust yet to be built with his defenders as he finds life harder without members of Barcelona's elite to find with the ball at his feet.
Bravo's vulnerability has also been noted by opposition supporters and he will need to learn to block out the jeers that will come his way when he is in possession.
In his defence, and to stop him simply becoming an easy target on occasions when it goes wrong, he was not responsible for either goal and there were plenty in front of him who have to take their share of responsibility for City's first league defeat.
The good news is he will know he has the backing of Guardiola, who has shown such faith in Bravo and believes he will prove that £17m was money well spent.
Guardiola's work in progress
Guardiola was right to provide some sobering context to this defeat. City have made a magnificent start under his stewardship but in real terms he has barely walked through the door.
The jury may be out on Bravo but elsewhere he has bought well. Stones was an honourable exception to Sunday's defensive struggles while Nolito, Ilkay Gundogan and Leroy Sane will add unquestionable quality.
Guardiola, however, is currently presiding over an ageing defence and the creaks are showing in 31-year-old Pablo Zabaleta, a magnificent City servant, and Kolarov at 30. Bacary Sagna, 33, was back-up on the bench along with 31-year-old Gael Clichy.
To add further mitigating circumstances, Guardiola was without arguably his most potent creative influence in the injured Kevin de Bruyne while the return of a injury-free Vincent Kompany will be welcome.
Guardiola will probably need another two transfer windows to make this his City side - the fact they have started so brilliantly is testimony to the instant impact he has had at Etihad Stadium and on the Premier League.
A full and firing City, working to Guardiola's principles, still have the talent to grace the Premier League this season and they are unlikely to run into many teams as driven and full of desire as Spurs were on Sunday.
Guardiola's measured response was just right. This was bound to happen - and he has shown in the past he is a very fast learner.