LONDON, ENGLAND - NOVEMBER 15: Dominic Thiem of Austria celebrates match point during his round robin match against Stefanos Tsitsipas of Greece during their first round robin match on Day one of the Nitto ATP World Tour Finals at The O2 Arena on November 15, 2020 in London, England. (Photo by Clive Brunskill/Getty Images)Clive BrunskillGetty Images