Greece's Stefanos Tsitsipas plays a forehand return to Bosnia's Damir Dzumhur during their men's singles match of the ABN AMRO World Tennis Tournament. (Koen van Weel/ANP/AFP)

ROTTERDAM, Netherlands: Rising Greek star Stefanos Tsitsipas said he "lost to himself" after suffering a shock defeat at the ATP event in Rotterdam by Bosnian Damir Dzumhur on Wednesday (Feb 13).