Graham Potter saw Chelsea’s performance against Borussia Dortmund as a “step forward” despite their 1-0 defeat in Germany.
The Blues need to pull off a second-leg comeback at Stamford Bridge if they are to reach the quarter-finals of the Champions League.
The first-leg loss continued their disappointing run of results under head coach Potter, but they were the better side for much of the match.
Potter said: “Overall, we were pleased with the performance for big parts of the game.
“We need a little bit of luck maybe and I thought we deserved a goal.
“But it’s only half-time and now we look forward to Stamford Bridge. We focus on the positives and it’s a step forward for us.
“The spirit is there in the team. We just need a little bit of luck and we need to carry on the performance level that we had tonight and keep improving. That’s the job.”
Karim Adeyemi scored a brilliant goal for Dortmund just after the hour mark – against the run of play and following a Blues corner at which the offside flag was raised but the referee played an advantage.
Ademyi ran onto Raphael Guerreiro’s flick-on and galloped fully 70 yards, beating Enzo Fernandez in the process, before rounding keeper Kepa Arrizabalaga and slotting home.
The lively Joao Felix had two great chances for Chelsea in the first half but could not find the target after linking up with Hakim Ziyech, and then hit the bar after being set up by Kai Havertz.
Chelsea continued to create openings after going behind and were denied by a terrific clearance off the line by Emre Can with 11 minutes remaining.
After Ruben Loftus-Cheek pulled the ball back to Kalidou Koulibaly, keeper Gregor Kobel got a touch to the defender’s shot but the ball was on the way in when Can slid in to hook it away.
And in the final seconds, a Fernandez strike was brilliantly saved by Kobel.