Chelsea edged into the Uefa Conference League semifinals on Thursday when a 2-1 home defeat by Legia Warsaw was enough for a 4-2 aggregate win.
Chelsea went 1-0 down to a 10th minute penalty before Marc Cucurella's close-range equaliser on 33, but French defender Steve Kapuadi put the Poles ahead again in the 53rd minute with what proved to be the winner on the night.
Legia had a lively following at Stamford Bridge with flares and shirtless chanting from around 1 000 clearly delighted fans.
Thanks to their 3-0 win in Poland a week ago Chelsea however will next face Sweden's Djurgardens, who thumped 10-man Rapid Vienna 4-1 away in extra-time their second leg.
A penalty by Czech forward Tomas Pekhart gave Legia the lead before Cucurella levelled and then saw a goal ruled out by VAR before Kapuadi's winner.
The manner in which Chelsea were defeated at home by the team currently fifth in the Polish Ekstraklasa, does not bode well for their Premier League top-five bid as coach Enzo Maresca's problems continued to mount.
But Chelsea remain favourites to join Roma, West Ham and Olympiakos as winners of the third-tier European competition.
Twice runners-up Fiorentina drew 2-2 in a see-saw match with Slovenians Celje, going 1-0 up in the first half before slipping to 2-1 down with on form Moise Keane scoring the clincher for a 4-3 aggregate win.
In their semi they face in-form LaLiga side Real Betis who drew 1-1 at home to secure a 3-1 aggregate win over Jagiellonia Bialystok of Poland.