The Gunners were surprisingly beaten 3-1 by the French club in the first leg of the Champions League Round of 16 at the Emirates Stadium with inefficiency in front of goal and poor defending the major contributing factors.
After the match, Wenger blamed these two facets of Arsenal's game on the defeat which has them in a very precarious position for the return leg at the Stade Louis II on March 17.
"We had both aspects wrong: we had chances that we did not take and were suicidal defensively because we were open on the second and third goals," said the Frenchman who is Monaco's longest-serving manager.
"We knew at half-time it was important to keep our nerve and with the vast experience we have through this competition, we knew we could not afford this. And so on that front we are guilty."
Alex Oxlade-Chamberlain gave the Gunners some hope with a lovely curling goal in injury-time but the north Londoners self-destructed in the 94th minute when allowing Yannick Ferreira-Carrasco to slot beyond David Ospina after winning the wall in midfield.
Of 2-1 scenario, which Arsenal happened to find themselves in, Wenger added: "Even at 2-1 how can we with one minute to go just leave the whole half open? It is difficult to understand.
"We controlled the game quite well, but with their first shot they scored a deflected goal. Everything went for them tonight, but on top of that you see as well why Monaco have done well in the group stage. They are well organised and physically very strong, they did not weaken through the game, but we did."
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