Janko Tipsarevic defeated Andy Murray 6-3 6-4 in an exhibition match in Abu Dhabi on Thursday.
The world number three was below par as the Serbian progressed to the semi-finals of the Mubadala World Tennis Championship.
The match progressed on serve until Murray was broken in the fourth game by Tipsarevic, who went on to take the set.
Murray opened the second with an ace, but Tipsarevic, who is ranked ninth in the current ATP standings, hit back to pile on the pressure by claiming an immediate break of serve.
The set moved on with the reigning US Open champion trailing the 28-year-old at 5-3 after some loose play.
Serving to stay in the match, the Scot handed the advantage to his opponent with a double-fault, before a cross-court winner and shot down the line helped him on the way to making it 5-4 in the second set.
Tipsarevic was therefore given the chance to serve for victory and earned himself two match points as Murray was unable to clear a smash to the baseline.
"I'm looking forward to training very hard and playing some of my best tennis next year," said Murray.
"I hit the ball pretty well, it was just the execution of some of my shots wasn't perfect, but that's pretty normal when you have not played a match for a while."
Nicolas Almagro awaits the winner in the last four after he came in as a late replacement following the withdrawal of Rafa Nadal due to illness.