Roger Federer says Rafael Nadal "challenged me in ways no one else could" as he paid tribute to his former long-time rival ahead of his retirement this month.
Nadal, a 22-time Grand Slam champion, will call time on his glittering career which spans more than two decades at the Davis Cup Finals in Malaga this week.
Twenty-time Grand Slam winner Federer, who retired after playing doubles with Nadal at the Laver Cup two years ago, faced the Spaniard a total of 40 times across 15 years with their rivalry being one of the greatest in tennis.
"As you get ready to graduate from tennis, I've got a few things to share before I maybe get emotional," Federer wrote on X.
"Let's start with the obvious: you beat me - a lot. More than I managed to beat you. You challenged me in ways no one else could.
"On clay, it felt like I was stepping into your backyard, and you made me work harder than I ever thought I could just to hold my ground.
"You made me reimagine my game - even going so far as to change the size of my racquet head, hoping for any edge."
In 2004, Nadal, who was 17-years-old at the time, beat Federer in their first meeting. The Spaniard would go on to win 24 of their 40 matches with the Swiss victorious in 16.
Their final encounter was at Wimbledon in 2019 when Federer, then 37-years-old, triumphed.
"Rafa, you made me enjoy the game even more," Federer added.
"OK, maybe not at first. After the 2004 Australian Open, I achieved the #1 ranking for the first time.
"I thought I was on top of the world. And I was - until two months later, when you walked on the court in Miami in your red sleeveless shirt, showing off those biceps, and you beat me convincingly.
"All that buzz I'd been hearing about you - about this amazing young player from Mallorca, a generational talent, probably going to win a major someday - it wasn't just hype.
"We were both at the start of our journey and it's one we ended up taking together. Twenty years later, Rafa, I have to say:
"What an incredible run you've had. Including 14 French Opens - historic! You made Spain proud... you made the whole tennis world proud."
In 2022, Federer joined forces with Nadal for the final match of his career and played in the doubles for Team Europe against Team World's Jack Sock and Frances Tiafoe at the Laver Cup.
The pair were famously pictured crying together at the event.
"[...] And then there was London - the Laver Cup in 2022. My final match," Federer continued.
"It meant everything to me that you were there by my side - not as my rival but as my doubles partner.
"Sharing the court with you that night, and sharing those tears, will forever be one of the most special moments of my career.
"Rafa, I know you're focused on the last stretch of your epic career.
"We will talk when it's done. For now, I just want to congratulate your family and team, who all played a massive role in your success.
"And I want you to know that your old friend is always cheering for you, and will be cheering just as loud for everything you do next."
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