World number six Marin Cilic was handed a shock defeat in the warm-up event ahead of the Australian Open, with the top seed losing to France's Gilles Simon in the Maharashtra Open semi-finals in Pune, India on Friday.
World number 89 Simon, who beat third seed and defending champion Roberto Bautista Agut in the second round, was punished by Cilic for making a slow start and lost the first set before making a stunning comeback to win 1-6, 6-3, 6-2.
The former US Open champion was expected to have a strong start to the season ahead of the Australian Open, which begins on Jan. 15.
Several top players including Andy Murray and Kei Nishikori are out of the grand slam event due to injury while world number one Rafa Nadal and Serb Novak Djokovic remain injury doubts, leaving the field open for other top contenders to take advantage.
Second seed Kevin Anderson beat France's Benoit Paire 6-7(6) 7-6(2) 6-1 in a tough two hour and 20 minute encounter to reach his second final in as many weeks, after winning the Mubadala World Tennis Championship event.
Anderson and former world number six Simon will face off in the final on Saturday.