Tennis guru Nick Bollettieri says the US Open match between Serena Williams and Jennifer Capriati was "one of the worst nights in the history of tennis".
Capriati won 2-6 6-4 6-4 to reach the last four but the match was plagued by a number of dubious calls, notably from Portuguese umpire Mariana Alves.
Bollettieri said: "Serena got robbed six times during the last set.
"Every reporter watching, including John McEnroe, could not believe the quality of the umpiring."
He added: "You could see on the court Serena was holding back the frustration because it was one of the worst examples in the history of tennis umpiring."
Bollettieri, who has coached the likes of Andre Agassi, Jim Courier and Monica Seles, is at Flushing Meadows to see a number of his charges, past and present.
Wimbledon champion Maria Sharapova suffered a surprise loss to Mary Pierce but Tommy Haas has made it through to the quarter-finals.
The German is a Bollettieri Tennis Academy graduate and is approaching his best form again after a year out with a shoulder injury.
Outside of his own stable, Bollettieri has also been casting his eye over Tim Henman.
"I almost had Tim at the Academy," said the American, whose academy is based in Florida.
"It's one of the disappointments of my tennis career that I didn't get to work with him.
"If Tim had come to the Academy and didn't have the added pressure of being the English hope, he could have accomplished even more than he has.
"I don't know if he could have won a Grand Slam but I do know he's one gem of a young man."