Rafael Nadal and Novak Djokovic were knocked out of the ATP Finals as Daniil Medvedev and Dominic Thiem set up a title decider.
World number two Nadal served for the match at 5-4 in the second set but Russia's Medvedev hit back brilliantly to win 3-6 7-6 (7-4) 6-3 in London.
He was the more aggressive player throughout and was composed in the decider as errors came from Nadal.
Earlier, Thiem beat world number one Djokovic 7-5 6-7 (10-12) 7-6 (7-5).
The Austrian trusted his big hitting and fought back from a 4-0 deficit in the deciding third-set tie-break to win in almost three hours.