Daniil Medvedev fought back to beat Rafael Nadal and set up a title decider with Dominic Thiem at the ATP Finals.
Nadal served for the match at 5-4 in the second set but the Russian, 24, 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, third seed Thiem beat world number one Novak Djokovic 7-5 6-7 (10-12) 7-6 (7-5) in almost three hours.
He trusted his big hitting and fought back from a 4-0 deficit in the deciding third-set tie-break to win.