Serena Williams has revealed her admiration for Roger Federer, describing the 20-time Grand Slam champion as a "genius" and the "greatest player".
The debate over the GOAT (Greatest Of All Time) continues to rage on among tennis fans with Federer, Rafael Nadal and Novak Djokovic bidding for supremacy.
Federer and Nadal have both won 20 Grand Slam titles while world No 1 Djokovic, the youngest of the 'Big Three' at 33, is on 18.
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Federer, 39, is this week playing only his second tournament since returning to the ATP Tour in March after spending more than a year on the sidelines due to two knee operations.
"I think two words sum it up: Roger Federer," Williams said of Federer’s legacy at the Emilia-Romagna Open in Parma.
"He's just a synopsis of greatness and class and amazing and really changed the game. You see players playing like him, moving like him, doing his techniques. The guy is (a) genius."
Williams won the last of her majors at the 2017 Australian Open before becoming a mother and has since been chasing a 24th major title to equal Margaret Court's record.
On Monday, the American won her first match since losing in the Melbourne semi-finals in February and said she was a Federer "superfan".
"I just feel like he is really the greatest player," Williams said.
"You can't not like the guy, that's how I feel. His game is so fantastic. If I could only play like him."
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Top-seeded Federer will begin his campaign in Geneva later on Tuesday against Pablo Andujar, who said he has been looking forward to a match against the Swiss for a long time.
"It was something that I wanted, to have a match against Roger, just to tell my kids and my grandkids when I get older that I played him," Andujar told reporters.
"I think when you play Rafa, Novak and Roger...these guys became myths, (they are) something above the sport. I would say that the most important is that they grew the sport."
Additional reporting by Reuters
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