Karim Adeyemi’s brilliant breakaway goal for Borussia Dortmund means Chelsea have a 1-0 deficit to overcome following the first leg of their Champions League round of 16 tie
Graham Potter's side had the better chances amid a boisterous atmosphere in Germany but Thiago Silva had a goal disallowed for handball and Joao Felix hit the crossbar when well placed
 Ademeyi's solo run punished their earlier profligacy just after the hour mark
It was cruel on Chelsea given their performance
 Once behind they pushed hard for the equaliser and came close when Kalidou Koulibaly had his fierce shot cleared off the line by Emre Can
 But they must now come from behind at Stamford Bridge to progress
The defeat on the night means that Chelsea have now won only once in nine matches since the turn of the year and though Potter will have been encouraged by some of what he saw, this was further evidence that this is a team still finding ways not to seize victory
The Chelsea boss told : "The boys have been fantastic in terms of their work, but at the moment, we're suffering in terms of results
 But the performance was a big step forward for us tonight
"It's half-time
 We need to regroup and take the game at Stamford Bridge
"The relaxing of restrictions in the summer that had previously required temporary seating to be installed on the vast Sudtribune for European competition meant that the knockout stages of the Champions League were treated to the full Dortmund experience
The terrace was packed over one hour before kick-off, a cacophony of boos greeting the Chelsea players for their warm-up let alone the game itself
 With confidence fragile, cohesion fledgling, it made for a daunting test for Potter's team
They played on the counter-attack in the first half but there were opportunities
 Thiago Silva had a goal disallowed for handball from Reece James' left-wing free-kick before Joao Felix spurned two excellent chances to give Chelsea the lead on the break
The first saw his measured shot fly over the bar
 The second, on his weaker left foot, came back off the crossbar having been set up by Kai Havertz
 Along with the speedy Mykhailo Mudryk, Chelsea looked potent with space to run into but could not make it count
Dortmund, for all their first-half possession, had little clear-cut for Kepa Arrizabalaga to deal with, Sebastien Haller's shot on the angle being as close as they came
 Captained by the combative Jude Bellingham, they offered just enough to keep the crowd in it
The game flipped in the second half, Chelsea taking control and testing the goalkeeper through James, while Mudryk and Enzo Fernandez had efforts blocked
 Just as the momentum was with them, they were exposed at the back by Adeyemi
One-on-one with Fernandez, he outpaced the backtracking midfielder and rounded Kepa before slotting low into the net
 The noise inside the stadium was extraordinary
 The Chelsea players seemed in shock
 It is becoming an unfortunate habit
Dortmund were jittery thereafter as the away side tried to fashion an equaliser, Fernandez forcing a fine save from the excellent Gregor Kobel from the edge of the box
 But the Chelsea supporters in the stadium were left bereft by their team's failure to conjure a goal
Speaking the night before about the link between resources and results, Potter had observed that the beauty of football is that two plus two does not always equal four in this game
 Right now, Chelsea continue to look less than the sum of their expensive parts
"Overall, we were pleased with the performance for big parts of the game," said the Chelsea boss
"It is complicated away from home in the Champions League, a hostile environment against a team in a good moment
 In the second half, apart from one decisive action where we don't do well enough, I thought we were the better team
"Chelsea had been the dominant force in the second half when they were caught out on the counter-attack
 "Sometimes you can feel comfortable in a game but you are never comfortable at this level," added Potter
"It is a poor goal
 We have to do better, we were pushing at the time, the better team
 So to concede in that manner, we are all disappointed
 The players are honest, they can do better
 We have to help them with that
 But we have to focus on the positives
"The attitude has been really good as a group
 The spirit is there in the team
 We just need a bit more luck, carry on the performance level and keep improving
"Hopefully, we can improve and take the game to them at Stamford Bridge
"Adeyemi earned comparisons to the cartoon character Road Runner following his superb solo winner
"Meep Meep! And then he goes," Dortmund head coach Edin Terzic told  when asked to describe the 21-year-old's goal
"This is the quality of Karim
 It was a corner kick and we defended it quite well
 It was a dangerous situation but then when you see his acceleration
 His first touch was there to accelerate the game
"If you are quick like this then it is going to be very tough for every defence
 It was a great goal and very important as it was the winning goal
""Chelsea had everything but the goal," said Clinton Morrison on 
"They were really good and there are a lot of positives to take for Graham Potter, but they just could not put the ball in the back of the net
"They have bought a lot of players but not an out-and-out No 9 who can stick away a chance
 Chelsea will head back to London disappointed with the result, but Potter will be happy with the performance
 What was lacking was the cutting edge in the final third
"Joao Felix could have come away with the match ball on another night, but on the other hand Dortmund's Karim Adeyemi is hot property
 There will be a lot of big clubs in England and across Europe looking at him
 He has got a lot of pace and he caused Chelsea plenty of problems
 His goal was outstanding
"Chelsea are back in Premier League action on Saturday afternoon when they host the bottom club Southampton at Stamford Bridge
There are further Premier League games against Tottenham and Leeds before Chelsea welcome Dortmund for the return leg of this tie on March 7
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