This was probably the biggest game of Arsenal's season. To come out of it with a 2-1 defeat is a huge blow to Arsenal's ambition of finishing in the top four.
In many ways, it was a familiar experience for the Gunners: they dominated for long periods, but were undone by some dreadful defending.
There were, however, six new things we learned during the course of the game. Go to the next slide to discover the inferences we can draw from this derby defeat.
Arsene Wenger's Arsenal have been guilty of occasionally shambolic defending for several seasons now. The difference this year is that they are also weak going forward.
A team with top-four aspirations cannot afford to have a porous defence and a poor attack.
Last season, Arsenal's blushes were repeatedly spared by the brilliance of Robin van Persie. This campaign, they have no one to provide those moments of salvation.
Arsenal fans will lament two defensive errors, but the truth is that despite sustained possession, they never seriously threatened the Spurs' goal.
With Bacary Sagna out injured, many feared Carl Jenkinson would be cruelly exposed on the big stage.
In fact, Jenkinson turned out to be one of Arsenal's better players. With Gareth Bale chosen to play centrally, Jenkinson had plenty of room to get forward, and it was a big surprise when he was replaced by Tomas Rosicky.
Until that point, Jenkinson had been Arsenal's main attacking outlet. He played with all the heart and spirit of a true Arsenal fan.
The instant success of the likes of Santi Cazorla and Michu had banished the idea that players from La Liga require a period of adaptation. However, Arsenal full-back Nacho Monreal seems to be struggling to come to terms with the demands of the Premier League.
The injury to Kieran Gibbs has forced Monreal to be thrown in at the deep end, and he is suffering slightly. In Spain, he had a reputation as a solid defender, but he was arguably culpable for both Tottenham's goals on this crucial derby day.
After this poor display from Monreal, Kieran Gibbs will expect to reclaim his place as soon as he is fit again.
Arsenal captains have a habit of walking away from the club. Perhaps this summer Thomas Vermaelen will follow in the footsteps of Thierry Henry, Cesc Fabregas and Robin van Persie.
Since inheriting the armband, Vermaelen's performances have declined dramatically. His ability on the ball remains unquestioned, but he is plainly struggling with the tactical aspects of the game. His positioning is frequently off, and Arsenal are being regularly punished for his absentminded defending.
Perhaps he is already thinking of his next destination. Given his recent performances, selling Vermaelen would not necessarily be a bad thing for Arsenal.
With Olivier Giroud ineffective as the central striker, Arsenal were crying out for an alternative from the bench.
All season long, it's been clear they needed another striker, and yet Arsene Wenger inexplicably allowed the opportunity to sign one to pass him by in January.
The only player Arsenal signed in January was a defender, Nacho Monreal, and that buy was only prompted by a serious injury to Kieran Gibbs.
The club's failure to sufficiently strengthen the squad could prove very costly come May.
Despite a derby defeat that leaves Arsenal trailing Spurs by seven points, the season is far from over.
Arsenal's other rival for a Champions League spot, Chelsea, face a couple of North London derbies and an intimidating trip to Anfield.
Arsenal's fixture list, meanwhile, is rather more inviting. Furthermore, unlike Tottenham and Chelsea, the Gunners don't have any cup competitions to distract them from their primary goal of a top-four finish in the Premier League.
There is still plenty to play for.