Karim Adeyemi scored a brilliant solo goal to condemn Chelsea to defeat in their Champions League last-16 first-leg tie at Borussia Dortmund.
The Premier League side rued missed chances as Joao Felix shot over from a good position and then hit the crossbar in the first half.
Reece James also forced two fine saves out of Dortmund goalkeeper Gregor Kobel in the second half as the visitors grew in confidence against the hosts, who were themselves struggling to create many chances.
But Chelsea were undone on the counter midway through the second period when Adeyemi broke from inside his own half following a Chelsea corner, knocked the ball past Kepa Arrizabalaga before slotting into the empty net.
Chelsea, to their credit, pushed for an equaliser and Emre Can swept the ball right off the goalline as Kalidou Koulibaly's deflected strike looks certain to trickle into the net.
Enzo Fernandez thought he'd equalise in the last seconds of stoppage time but his goalbound long-range strike was stopped superbly by Kobel as Dortmund held on.
Defeat leaves Graham Potter's side with the task of overturning the tie when the two sides meet at Stamford Bridge on 7 March.
Positive Chelsea display undone by familiar attacking issues
Chelsea brought in eight new players during a busy January, yet this was another match that exposed their failure to sign an out-and-out striker.
Three of the Blues' big money arrivals started the game - Mykhailo Mudryk, Fernandez and Felix - with the others ineligible because of Champions League restrictions on the number of players who can be added to squads after the group stage.
All three certainly add to the Chelsea squad's quality but none have so far been able to provide the answer to their goalscoring issues.
Felix was outstanding in the first half in Germany and looked the most likely to make a breakthrough as he got into several good positions, but failed to capitalise.
It took almost an hour for Chelsea to manage a shot on target - when James' free kick was superbly saved. Dortmund were not much better, but showed the clinical touch when Adeyemi broke, powered past Fernandez and then Kepa before slotting into the net.
The travelling fans were left frustrated - as Chelsea were arguably the better side against hosts who had won their previous six games.
Chelsea haven't scored twice in a game since the start of November, underlining the enormity of their task in the return leg unless things improve significantly in the final third.