Taylor Fritz kept his cool in the face of an irate Daniil Medvedev to win the opening match of the ATP Finals in straight sets.

American Fritz recorded his 50th win of the year by beating Medvedev 6-4 6-3 at the season-ending tournament in Turin, Italy.

Russian fourth seed Medvedev broke a racquet in response to his poor serving and threw a second after a stroke of bad luck while break point down.

"I'm super happy with how I played today," said Fritz, who reached his first Grand Slam final at September's US Open.

Medvedev hit seven double faults in a tight opening set, including two back-to-back to give fifth seed Fritz set point.

Capping a calamitous service game, the Russian double-faulted again, and reacted angrily to going behind by smashing his racquet against his seat and the ground.

At the start of the second set, Medvedev earned his first break point of the match but slammed his backhand return into the net.

Further break points went unconverted for both players before Fritz capitalised on his third, with a mis-hit lob that landed on the line.

An irritated Medvedev then received a point penalty after he broke a courtside microphone by throwing his racquet.

As his behaviour unravelled he was booed by the crowd for his antics, which included holding his racquet by its head as he waited to receive a serve.