Chelsea's Europa League semi-final opponents Eintracht Frankfurt suffered a humiliating defeat in the Bundesliga just days before the second leg tie at Stamford Bridge.
The German outfit opted to rotate their squad for the trip to Bayer Leverkusen, with star striker Luka Jovic and key midfielder Sebastian Rode among those rested for the clash.
But it was an afternoon to forget for the Champions League qualification contenders as they were crushed 6-1 at the Bay Arena.
A double from Lucas Alario, plus strikes from Julian Brandt, Kai Havertz, Charles Aranguiz and an own goal from Martin Hinteregger condemned Adolf Hutter's side to their biggest defeat of the season.
Filip Kostic, who set up Jovic's goal in the 1-1 draw in the first leg against the Blues, scored for Frankfurt but it proved to be nothing more than a consolation.
It puts their chances of qualifying for next season's Champions League in doubt, with Leverkusen now level on points with fourth-placed Frankfurt.
Chelsea, meanwhile, secured their place in next season's competition with a 3-0 win over Watford, although they could be without N'Golo Kante for the second leg after he came off injured in the first half.
Maurizio Sarri's side have the advantage heading into the second leg in London on Thursday, after Pedro's strike secured an away goal at the Commerzbank-Arena.
