Great Britain's Davis Cup fate will be decided by the doubles match in their quarter-final against Germany after Cameron Norrie lost for the first time in the 2021 event.
Knowing victory would secure Britain's semi-final place, Norrie was beaten 7-6 (8-6) 3-6 6-2 by Jan-Lennard Struff.
Dan Evans beat Peter Gojowczyk to put Britain ahead in the best-of-three tie.
But Struff's win set up a decider where Joe Salisbury and Neal Skupski face Germany's Kevin Krawietz and Tim Puetz.
Britain, without the resting Andy Murray, are aiming to reach the semi-finals at the 18-team Davis Cup Finals for the second successive edition.