Four-up after 26 minutes at Newcastle United with two goals from Robin van Persie and one each for Theo Walcott and Johan Djourou, Arsenal's title challenge was gathering speed.
But what followed stunned the Gunners and left manager Arsene Wenger worried about the psychological damage it could inflict.
Five minutes after the break Abou Diaby was sent off for shoving Newcastle's Joey Barton to the ground.
With their momentum gone, Arsenal then completely fell apart as the home side scored four times in 22 minutes to grab an unlikely 4-4 draw. Barton netted twice from the penalty spot.
"Mathematically (we lost) two points, but psychologically the damage is bigger tonight because everyone is very disappointed in the dressing room," Wenger said. "Only the future will tell."
It would have been a long journey back to London for Wenger's side, particularly Diaby whose loss of composure was the catalyst for his side's implosion.
"Certainly, more psychologically than on the footballing side," Wenger said when asked if Diaby's rush of blood to the head had been crucial. "We were worried too much on protecting our lead after that because we were down to 10 men.
"Instead of continuing to play, we invited pressure. Afterwards we were very unlucky with some decisions as well. I cannot do anything about that."
Manchester United's later defeat by Wolverhampton Wanderers allowed Arsenal to close to within four points of the leaders but that would have been scant consolation for Wenger who also lost Djourou to a knee injury.
"It's very frustrating because we played a good game and we had an opportunity to take three points in the title race," Wenger added. "Newcastle kept fighting, I knew at 4-0 the game was not over because it was important to keep our nerves and continue to play."
Wenger said Diaby's red card was "completely unnecessary" but said Barton should not even have been on the pitch to tuck away the two penalties in Newcastle's epic fightback.
"It was a completely unnecessary sending off and I believe Barton was very lucky to stay on the pitch because of his tackle on Diaby," Wenger said.
"(Diaby) is very disappointed at the moment, it's better not to talk to him. He has to try to get over that. It's a shame because he had a great first half.
"(His reaction could be) explained by the fact that he has been injured so many times from bad tackles that he lost a little bit quickly his nerves. This boy has been out for a long time and many times. Certainly the tackler provoked his reaction."
While Wenger's immediate reaction to his side's capitulation was fairly restrained, he will be concerned that another certain win was frittered away.
Before Christmas they blew a two-goal lead against bitter rivals Tottenham Hotspur to lose 3-2 and at the end of last season, with their title hopes still alive, they conceded three times in the final 10 minutes to lose 3-2 at Wigan Athletic.
They also surrendered a two-goal lead against West Ham United last season, giving further ammunition to the critics who ac
