West Ham manager Manuel Pellegrini has expressed his disappointment at the manner in which his side conceded twice against Brighton and Hove Albion, following their 2-2 draw at the London Stadium.
Dale Stephens and Shane Duffy both took advantage of lacklustre defending from corners to give the Seagulls a surprise two goal lead.
Marko Arnautović managed to score twice in quick succession to salvage a point for the Hammers, but his boss was left upset with the team's defensive showing, considering they had restricted their opponents in open-play.
As quoted by West Ham's official website, Pellegrini said: "We're frustrated because we knew before the game that the most important way that Brighton score goals is from set-pieces, specifically corners.
"They had seven goals from corners and we worked on that, but we allowed them to score two goals. I do not remember one chance from Brighton to score otherwise during the whole game."
Despite his annoyance, the Chilean praised the side's character, having come from two goals down after creating very little in the way of chances in the first period.
"But, we didn't have one chance in the first 45 minutes on goal. After that, losing 2-0, I have to praise the spirit of the team.
"We didn't give up, we continued to fight, and we draw the game 2-2, and after that we had clear chances."
Having fallen two goals behind, Pellegrini introduced Mark Noble and Michail Antonio from the bench and both players had an instant impact. They provided an assist each for Arnautović, who latched onto Noble's cross-field pass to slot home his first, before receiving Antonio's pull-back to fire home the leveller.
Although they changed the complexion of the game, the Chilean explained that squad rotation had played a part in his team selection, before going on to praise the influence of the returning Arnautović.
"I think both Noble and Antonio came into the game very well. They changed the face of the team. We needed to make changes. We have played nine games with our matches since December.
"We needed to make the substitutes because it's impossible to keep playing matches with the same players.
"Marko rested for a complete month so he is full of energy. He is a decisive player in these types of games. He scored two goals and I hope he will continue in the way he did tonight.
"I think, fortunately for us, the spirit of the team was good after going 2-0 down. The strength was there to play better. Now we must try to qualify in the FA Cup against Birmingham, and then we recover for a week."