Slaven Bilic blamed a flat performance and a "very cheap goal" as West Ham were held to a 1-1 draw by Stoke in east London.
The Hammers struggled to get going before half-time but took the lead moments after a Bilic reshuffle as Michail Antonio's header deflected in off Glenn Whelan.
But Adrian gifted Stoke substitute Bojan an equaliser as he rushed from his goal and was beaten to a long ball by Jon Walters.
The error denied West Ham a third straight win in front of their own supporters, and Bilic told Sky Sports: "It was a mistake. Mistakes happen, and unfortunately he made one because he misjudged the timing.
"It was very cheap at a crucial moment of the game when you're 1-0 up and playing good. We knew they'd throw bodies up front and hit long balls but still...very cheap goal."
The Hammers boss was at a loss to explain his side's lack of threat, remedied only when he made a double change in the second half and sent Antonio and Ashley Fletcher to play as a two-man strikeforce.
"We looked sharp in training and in the last few games, and there was really no reason. We didn't have a midweek game. It was just...flat.
"A point is a point and it's a fair result but we were looking for three. It wasn't a good game of football and no team deserved to win.
"Our first half was flat - we didn't start on our front foot. In the second half we improved a lot. We changed it a little bit and we scored the goal.
"Until they equalised we played good and created some good moments but then we conceded - from our point of view - a very cheap goal and it cost us the result."