Arsene Wenger slammed his Arsenal flops as "naive and suicidal" after its defensive meltdown allowed Monaco to clinch a stunning 3-1 win in the Champions League last-16 first leg.

Wenger's side was widely expected to see off the French club and advance to the quarterfinals of Europe's elite club competition for the first time since 2010.

But instead it is on the verge of a fifth consecutive last-16 exit following an incredible meltdown at Emirates Stadium on Wednesday.

Geoffrey Kondogbia's first-half strike was followed by a cool finish from former Tottenham forward Dimitar Berbatov and, although Alex Oxlade-Chamberlain got one back for Arsenal in the 90th minute, there was time for Yannick Ferreira-Carrasco to score Monaco's third and leave the Gunners needing a huge effort in the second leg on March 17.

In the heat of an immediate post-match media conference, Wenger is usually composed enough to deflect questions that ask him to criticise his players.

But after one of the most chastening defeats of his 19-year Arsenal reign - at the hands of the club where he made his managerial reputation - the 65-year-old was unable to conceal his frustration.

Taking aim at the careless play of Arsenal's defenders and the needlessly gung-ho attitude of the rest of the team, he said: "It was a horrible night. We missed chances and were a bit suicidal defensively.

"Their first goal was unlucky with the deflection, but the second and third were suicidal. We cannot give away the third goal like we did.

"The balance wasn't right and when we lost the ball we were exposed. I was most disappointed by our defensive naivety.

"It looks like we lost our nerves and our rationality. The heart took over the head ... and at this level that doesn't work.

"Mentally we weren't sharp enough to get into this game, and we paid for it."

After getting its domestic form back on track in recent weeks, this was a return to the kind of mentally fragile and defensively sloppy display that has so often ruined Arsenal's hopes in Europe in the Wenger era.

And Wenger suggested his players might have taken victory for granted.

"I hope we weren't complacent, but it looks when you have no sharpness that anything is possible," he said.

"We rushed our game. The difference was the mentality, we were too impatient because this is a game of 180 minutes."

Miraculous escape

Arsenal now needs a three-goal victory to complete a miraculous escape in the return game at the Stade Louis II.

But Monaco has not conceded three goals at home in any match this season and no team has lost a Champions League first-leg knockout tie at home by two goals and progressed to the next round since Ajax in 1969.

"The task is massive now. The third goal makes it even more difficult," Wenger said.

"We have a much smaller chance but no matter how big the size is we will go for it."

After a fairly underwhelming Ligue 1 campaign, this was a remarkably mature and clinical display from a Monaco team missing several key players.

It was such a stunning victory that it even received royal approval, with Prince Albert of Monaco joining the players on the pitch to celebrate at fulltime.

Monaco boss Leonardo Jardim said he felt Arsenal would be vulnerable if his side could survive the early storm.

"We analyzed Arsenal beforehand and we knew they have been a lot stronger in the first half and struggle a bit after the interval," he said.