World No.4 Stefanos Tsitsipas crashed to defeat in his first singles match since elbow surgery on Monday, losing an epic battle with feisty Argentinian Diego Schwartzman 6-7 (5/7) 6-3, 6-3 at the ATP Cup.

The Greek star went under the knife in late November after pulling out of the ATP Finals in Turin, hoping to be at full fitness for the Australian Open later this month. He was scheduled to return against world number nine Hubert Hurkacz at the teams event on Saturday, but withdrew before the match, opting instead to ease himself back in a doubles rubber.