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.