Defending champion Andy Murray was knocked out of the Sony Open in Miami at the quarter-final stage by Novak Djokovic, who claimed a 7-5 6-3 win.
In their first match since last year's Wimbledon final where Murray triumphed, Djokovic was the victor, although the game hinged on a controversial moment in the first set, when the Serb was leading 6-5.
With Murray serving to stay in the set Djokovic advanced and appeared to play the ball before it passed over the net - which is against the rules.
The moment was a turning point and although the point stood, Murray seemed to be unable to put it to the back of his mind and lost the game against his serve, with Djokovic duly claiming the first set.
The world number two then wrapped up the second set in comfortable fashion, with Murray still discussing the controversial moment deep into the contest.
The match went on serve in the first set - although Murray had to fight to hold in the fourth game - until the controversial moment swung the momentum into Djokovic's favour.
Murray was serving to level at 6-6 when Djokovic rushed forward and appeared to hit the ball while his racquet was over the net and not on his side of the court.
Murray complained to the chair umpire but his protests fell on deaf ears, and Djokovic duly claimed the game to love to take the first set 7-5.
The Scot continued his protest in between sets but to no avail, and his Serbian opponent was on top as he quickly served to claim a lead in the second.
However, the match settled down and the two men matched each other game for game until Murray broke Djokovic in the fifth, only to suffer a break of his own serve in the very next game.
Djokovic broke again to take a 5-3 lead and served out the next game to love to claim the second set and the match 7-5 6-3 in one hour and 30 minutes.