Marcel Schmelzer has blamed costly "individual errors" for Borussia Dortmund's surprise 3-1 defeat at Hamburg on Friday.
Dortmund had only lost once in the Bundesliga this season heading into the match at the Volksparkstadion but rarely looked like earning the win that would have seen them close to within two points of leaders Bayern Munich.
Pierre-Michel Lasogga opened the scoring from the penalty spot 19 minutes in and Lewis Holtby doubled the hosts' advantage just before the break.
An own-goal by Mats Hummels ultimately put the match beyond the visitors despite Pierre-Emerick Aubameyang's late consolation and Schmelzer feels Thomas Tuchel's side made too many errors and failed to take their chances.
"I think we played really poorly in the first half," the left-back said. "We allowed our opponents far too much room and didn't make the most of our opportunities in their half.
"We made a lot of individual errors. We've got to look at ourselves.
"We expected a lot of ourselves following the international break and didn't deliver on what we wanted to do."
Goalkeeper Roman Burki was similarly unimpressed, labelling the performance as one of their worst this season.
He added: "It's difficult to work out what happened so soon after the game. We weren't aggressive enough today. It was one of our worst games this season and we only have ourselves to blame."