Andy Murray was beaten in straight sets by Janko Tipsarevic at an exhibition tournament in Abu Dhabi on Thursday.
Murray, the world number three, looked off his game as he fell to a 6-3 6-4 loss against Tipsarevic on the opening day of the Mubadala World Tennis Championship.
The Serbian progressed to the semi-finals with the victory, where he will face Spain's world number 11 Nicolas Almagro, who came in as a late replacement following the withdrawal of Rafael Nadal due to a stomach virus.
The match started off fairly evenly and continued on serve until Murray was broken in the fourth game by Tipsarevic, who went on to take the first 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 progressed with the reigning US Open champion trailing the 28-year-old at 5-3.
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.
However, Tipsarevic held his nerve on serve to set up a last-four clash with Almagro.
After the match, Tipsarevic told ESPN: "I am happy with my game. I know it's an exhibition match but it's not every day you get to play a grand slam champion and an Olympic gold medal winner. I'm just happy I managed to play good tennis tonight."
Murray added: "I'm looking forward to training very hard and playing some of my best tennis next year. It's nice to play in events like this and it's a great atmosphere to play in."