Thomas Tuchel admits Borussia Dortmund were not "physically and mentally" fresh following their late surrender in a 2-1 defeat at Cologne on Saturday.
Sokratis Papastathopoulos' 18th-minute header put Dortmund in front at the RheinEnergieStadion and it appeared as though they would weather a Cologne storm as the clock wound down.
However, Simon Zoller took full advantage of a poor error from Dortmund goalkeeper Roman Burki to hammer home the equaliser seven minutes from time, before Anthony Modeste ended a two-month goal drought with a dramatic last-minute winner.
It was just Dortmund's third Bundesliga defeat under Tuchel and the collapse means they are eight points adrift of leaders Bayern Munich heading into the mid-season break.
"I wish that we could have finished the game in the first half," Tuchel said. "We had to try and achieve the second goal, we missed the chance to do that.
"We pulled back completely in the second half unfortunately and almost of our possession was in our own half, we not as aggressive and brave as we were in the first half.
"Cologne's counter-attacking was extremely passionate. We were mentally and physically not so fresh."
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