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 in Tuesday's victory.
The 28-year-old Russian, who had been booed for his antics against Fritz, 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.
"I went into this match blocking the noise, even from myself," said 2020 champion Medvedev.