Bayer Leverkusen slumped to a 2-1 home loss to Cologne on Friday to end their 14-game unbeaten run across all competitions and put their European spot in danger with three Bundesliga matches remaining.
Cologne's Davie Selke struck twice in the first half - either side of Amine Adli's equaliser - to give them their third-straight away win, their longest winning run away from home in 31 years.
It was not the dress rehearsal that Xabi Alonso's Leverkusen team had been hoping for ahead of next week's Europa League semifinal first leg against AS Roma.
They are on 48 points in sixth place, which would be good enough to secure a spot in next season's Europa Conference League, two ahead of Mainz 05 and VfL Wolfsburg, who face Borussia Dortmund on Sunday.
Selke stunned the hosts in the 14th minute, easily beating defender Jonathan Tah to head in and give Cologne the lead with their first chance of the game.
Leverkusen levelled with a perfectly executed counterattack that ended with Adli slotting in.
The hosts were in full control of the game when Cologne struck again as Selke stabbed in his second goal of the evening in the 36th minute against the run of play.
Bayern Munich, in top spot on 62 points, face Werder Bremen on Saturday. Dortmund are a point behind.