Arsenal boss Mikel Arteta admits his players failed to perform after going 2-0 ahead after their 2-2 draw at West Ham.
It was a repeat of the result a week ago at Liverpool.
Arteta later said: "We started extremely well again - dominated the game, dominated the pitch and scored two beautiful goals. After that, we made a huge mistake to stop playing with the same purpose to score the third and just think we could play around them and maintain that result. It looked too easy and at that moment we gave them hope and they took it.
"They did what they did really well - they started to play extremely direct, with long throws and winning corners. We really struggled to get out of that game. If you don't defend your box the way you should, with the two goals we conceded, you have to do many things much better for longer periods in the match. There was another moment, where you can go 3-1 up after 50 minutes, and the game is probably over then two minutes later, you concede a goal. But this is part of football.
"My worry is after 2-0, we made that huge mistake and didn't understand what the game required in that moment.
"It's easy to do it from outside the pitch. You have to be a player, and feel it there. We have to understand those emotions as well. We needed that ruthless mindset in that moment to go and kill the team. When a team is there for the killing, you have to kill it. Today we haven't done it. When you don't do that in the Premier League, at some stage they're going to turn around and have some momentum. Then you have to defend much better, for example with the second goal. If you don't, you won't win the game."
On if there was a psychological hangover from Anfield, Arteta also said: "It can happen but again, what goes through every mind is probably different. At half-time we all knew what we had to do and what we had to do better. Credit to West Ham - when they started to play their game. If they are efficient in those first two goals, it is difficult because you have to fight and earn the right to play.
"But when we did it, especially with the changes, we had to have more composure to finish the game."