France's Jo-Wilfried Tsonga accused a chair umpire of favouritism towards Rafael Nadal after the Spanish world number two won a marathon three-setter to reach the Miami Masters semi-finals.
Tsonga claimed that match official Damian Steiner was reluctant to over-rule calls affecting Nadal, causing him to pay close attention to rulings as well as his own on-court performance.
The Frenchman made his feelings known at 4-4 in the final set.
"I was complaining because all the match I have to challenge, and I was right, many, many times," said Tsonga.
"He never takes the initiative when it's against Rafa. So I have to be really focused on the ball. If it's really close, he would never say out against Rafa. If Rafa don't like him anymore, he would not be in the chair many times in the final and semi-final."
Nadal said after his 6-2, 5-7, 6-4 win that he understood why his opponent was getting upset, but that he also suffered from bad calls.
"I understand the frustration because it's true that the referees with the Hawk Eye are doing less overrules than before. I said (this) hundreds of times," said Nadal.
"But it is not because he's playing against me. No. Happen to me a lot of times."