Arsene Wenger was left speechless and mystified after watching Arsenal contrive to throw away a 2-0 lead at home to Tottenham on Saturday.
Samir Nasri and Marouane Chamakh had put the Gunners in complete control as they looked set to leapfrog Chelsea.
However, Spurs - who had just one Premier League away victory over their old rivals, in May 1993 - regrouped for the second half following the introduction of fit-again England striker Jermain Defoe.
Gareth Bale pulled a goal back on 50 minutes, before an inexplicable handball from captain Cesc Fabregas from a free-kick gave away a penalty, which Rafael van der Vaart converted.
Arsenal were then condemned to successive home league defeats for the first time in 13 years when Younes Kaboul headed in a dramatic late winner.
"If you look at the stats and the numbers, it is very difficult to understand how we lost this game - a drop in concentration, some basic errors, some back luck as well," lamented Wenger, whose side were also beaten 1-0 at Emirates Stadium by Newcastle a fortnight ago.
"You are a bit speechless to re-analyse the game. It is a mystery how you can lose a game like that.
"If you look at the clear-cut chances that Tottenham had today, it is difficult to understand how we can concede three goals, but we lost it and we can only look at ourselves.
"We could not maintain the focus nor the urgency for 90 minutes because some players dropped.
"I believe that overall we delivered a performance expected in a game like that quality-wise.
"However, it was a mixture of fatigue in the second half, and also a lack of cautiousness."
Despite the disappointment of the defeat to their fiercest rivals, Wenger insisted the title race was still wide open.
"There are 10 teams who can win the championship mathematically. Tottenham is one of them," the Arsenal manager said.
"I am convinced we are in it, but there are chances in the championship you want to take."
However, the Gunners boss insisted his team cannot now afford to lose any more games at Emirates Stadium, having also gone down to West Brom in September.
"Three home defeats are three too many," Wenger said.
"The first two games we didn't deliver a performance and you can only say that we got what we deserved.
"However, today we delivered the performance.
"What is worrying for me is that we had an opportunity to go top of the league and when you have to deliver, we can't. That's worrying because that's part of our job."
Wenger added: "We put ourselves in the right position and we failed, so we have to accept that. That is mental more than football.
"Today we were always in a position where we could have won the game, and that is difficult to swallow."
