Despite racing into a two-goal lead, Bayer Leverkusen were quickly pegged back and made to settle for a 2-2 draw against CSKA Moscow.
Admir Mehmedi and Hakan Calhanoglu had the Werkself cruising after 15 minutes, and looking like they wouldn't be caught.
However, Alan Dzagoev and Roman Eremenko scored twice in three minutes to draw CSKA level but neither side could find the crucial fifth goal.
Early openings for Bayer
Both teams remained largely unchanged after their weekend outings, with Leverkusen bringing in Julian Brandt for the injured Karim Bellarabi; CSKA stuck with the same 11.
The hosts heaped early pressure onto the crumbling Russian rearguard and were duly rewarded in the opening stages. A superb through ball from Benjamin Henrichs found Mehmedi inside the area, and the Swiss forward made no mistake with his finish past Igor Akinfeev. He was slightly offside, yet the goal still stood.
Bayer didn't have to wait long to add their second, as Kevin Kampl's cross was finished off by Calhanoglu. His left-foot drive took a deflection which left the already beaten Akinfeev with no chance, in a score-line that quickly had CSKA wondering what had happened in the first quarter of an hour.
CSKA turn the game on its head, second half fails to spark
However, Leverkusen's inability to kill the game off ultimately cost them dearly. Brandt, Wendell and most notably Mehmedi again failed to grab an all-important third. Moments later, the old adage about a two-goal lead being the most dangerous in football rung true.
An injection of pace from CSKA finally shook up their hosts, as Aleksei Ionov shifted the ball into Dzagoev before he left Jonathan Tah for dead and did just the same when finishing past Bernd Leno. The jitters had kicked in and Lacina Traoré took full advantage to play in Eremenko to calmly slot home. Leverkusen were shocked.
The second half was open but nothing like the first, with neither 'keeper being truly tested. The main worry for the hosts will be that Lars Bender had to come off injured early in the second period, which is another setback he most certainly does not need.
Otherwise, it is a blow to the morale that had been so high after Saturday's comeback and a major missed chance to get ahead of the rest in their group. For CSKA, they deserve huge credit for turning around a seemingly lost cause and not letting their heads drop.