Rafael Nadal's Dubai Open title defence unravelled as he crashed out 7-6 6-2 to Mikhail Youzhny in the quarter-finals.
Nadal (left) also lost to Youzhny in the US Open quarter-finals last season
The world number two lost the first set tie-break when a Hawkeye replay upheld Youzhny's claim a drive was in.
The Russian broke serve for 4-2 in the second and although Nadal saved a match point, Youzhny sealed the set.
World number one Roger Federer also reached the last four, beating Serbia's Novak Djokovic 6-3 6-7 (5-7) 6-3, and will now play Germany's Tommy Haas.
Fifth seed Haas, who won last week's Memphis Open, thumped Belgium's Olivier Rochus 6-0 6-2 for his 11th straight win and 16th in 18 matches this season
Sweden's Robin Soderling battled past France's Fabrice Santoro 6-1 6-7 6-0.
Maybe I should have closed it out earlier - I can only blame myself
Nadal angrily threw down a ball and remonstrated with the umpire after Hawkeye overruled the line judge's decision in the first-set breaker.
He complained after the defeat: "I said, 'look the ball is out' and the umpire said 'I know'.
"The mark was clearly there but Hawkeye said it was in. It's unbelievable."
Regardless of the controversial call, Nadal was not at his best during the match and failed to find much penetration with his heavy topspin.
The Spaniard has still not reached a final since Wimbledon eight months ago.
Hawkeye's replay technology also played a part in Federer's victory because without it he would have won in straight sets.
Though top seed Federer achieved his 39th successive win, he lost a tie-break for the first time in 16.
On the second of a pair of match points in the tie-break the line judge called Federer's drive in, a decision which would have given him a straight sets win.
But the world number 14 appealed to the replay, which showed Federer's shot was out, and two points later Djokovic stole the set with a net cord.
Federer said: "It's hard to accept at match point. But maybe I should have closed it out earlier not to be in that position, I can only blame myself."
Seventh seed Djokovic, 19, stepped up a gear at the start of the deciding set while Federer struggled with his forehand.
But the Swiss broke after two missed forehands from Djokovic before Federer served out for the match with little difficulty.