When Shkodran Mustafi rose above the Spurs defence to head home Mesut Ozil's free kick, everyone was left wondering who had rewritten the script. Arsenal were supposed to be walked over by a recently-rampant Spurs and yet here they were... losing.
Just before halftime, Hector Bellerin found Alexandre Lacazette in space on the right. Flashing the ball along the six-yard box, the Frenchman found Alexis Sanchez at the near post who gleefully lofted the ball over the onrushing Hugo Lloris. The game was over. The narrative lay in tatters.
On Saturday, Spurs get the chance to repay the favour when Arsenal visit Wembley for the second leg of this Premier League fixture. Here's how Mauricio Pochettino should set up his side to beat the old enemy.