A rejuvenated Daniil Medvedev defeated Alex de Minaur 6-2 6-4 in his second match at the ATP Tour Finals.
Fourth seed Medvedev was irate during his opening defeat by American Taylor Fritz on Sunday but looked far more settled during Tuesday’s victory.
The 28-year-old Russian, who had been booed for his antics against Taylor, put his fingers in his ears after sealing victory,
He lost only nine points on his serve as he wrapped up the win in an hour and 18 minutes.
Medvedev’s temperament was under scrutiny after his surly behaviour 48 hours earlier but he struck the ball superbly and broke in the third game with a cross-court winner.
The 28-year-old gained a double break when De Minaur double faulted, and went on to take the first set in 40 minutes.
De Minaur battled in a pulsating second set but Medvedev’s stunning backhand put him 5-4 ahead and he held serve to clinch victory.
Top seed Jannik Sinner – who beat De Minaur on Sunday – faces Fritz before the Italian’s home fans in Tuesday’s later Ilie Nastase Group match from 19:30 GMT.
Meanwhile, Britain’s Henry Patten and partner Harri Helioevaara are on the brink of the doubles semi-finals after a second straight victory.
They beat Australians Max Purcell and Jordan Thompson 7-6 (7-3) 7-5 in a repeat outcome to their Wimbledon final.
The British-Finnish duo are bidding to become the first team to capture the Wimbledon and ATP Finals trophy in the same season since Mike Bryan and Jack Sock in 2018.