Thiem victorious in ATP Finals opener, beats Tsitsipas in rematch of 2019 final

Dominic Thiem outlasted Stefanos Tsitsipas in a rematch of the 2019 final, beating the defending champion 7-6 (5), 4-6, 6-3 Sunday in the opening singles match at the ATP Finals inside a largely empty O2 Arena in London, England.