PARIS -- In the early stages of his career, Roger Federer had a problem with left-handers. He lost four of his first seven matches, and eight of his first 20, against them. Something about the different spin, the different look, threw him off.
Over time, as he honed his game to become the world's best player, he learned how to deal with it. Now he has a problem with just one of them: Rafael Nadal.
"I used to hate it," Federer said at Roland Garros, where he will meet Nadal in the semifinals on Friday, weather permitting. "Now I love it, you know, because it's a huge challenge against those guys, and he's the best one that I ever faced. I'm looking forward to the test."
Helped by his switch to a bigger-headed racket in 2014, Federer now drives through Nadal's serve, with topspin, where once Federer tried to slice it back after it kicked up high to his backhand. In their recent battles, he has been more successful on returns; in the final in Australia two years ago, he hit eight backhand winners in the final set alone, having hit only six in the four previous sets.
Like Novak Djokovic does, Federer also targets the Nadal forehand when he returns on the backhand from the ad-court, stopping the left-hander from playing from his favorite position on the court: just to the right of the center line, hitting inside-out forehands.
It is a tactic that has worked superbly.
"That's one of the two big differences on why he [Federer] beats Rafa the last [five] times," Patrick Mouratoglou, Serena Williams' coach, told ESPN.com in Paris. "He stopped returning with slice on the backhand, and in the rallies, every time Rafa was playing a bit shorter, he would step in and hit the ball on the rise, so that's a big difference."
From being bullied around the court by the Nadal forehand a decade ago, Federer now attacks throughout. He comes to the net, serves and volleys at times, mixes things up and even uses the drop shot, a stroke he once called a "panic shot."
That's what it takes to beat Nadal.
But -- and it is a big "but" -- Friday's semifinal is on clay, on Court Philippe Chatrier, where Nadal has lost just twice in his career and won the title a record 11 times. The pair have not played each other on clay since 2013 and have not met in Paris since 2011.
The world's best players, in any sport, are masters in short-term memory loss, able to forget recent defeats and focus only on the next chance to win. Nadal is no different.
"If I had played him two, three times in Madrid, Monte Carlo, Rome ... I could tell you how I feel about him, see him right now," Nadal said, asked to assess Federer's game. "But I haven't played him recently ... so these things, I would feel them on the court, and it's been many years we have been playing against each other [on clay].
"We are in semifinals ... and we are part of the four best players of the tournament. That's the reality. Beyond [that], I cannot tell you anything. The semifinals are always very difficult matches, whatever the opponent. And with Roger Federer, I know it's going to be even one step higher."
On clay, Nadal has made Federer's life miserable, winning 13 of their 15 matches, including five at Roland Garros, four of them in finals. As Dominic Thiem, the Austrian also still going strong in Paris this year, said in Madrid recently: "If it was not for Rafa, I think Roger would probably have won four or five French Opens."
Federer's overall record against left-handers is 131-36, winning the past 21, a run dating back to a loss against Albert Ramos-Vinolas in Shanghai in 2015. But facing someone who hits with the other hand, uses different angles, plays with different spin, is a challenge, especially if it's Nadal.
Federer's lone French Open title came in 2009, when he beat Robin Soderling in the final after the Swede had taken out an ailing Nadal in the fourth round. Ten years on, having not played in 2016 due to injury and skipping Paris in 2017 and 2018, the Swiss is back in the semis at age 37 and again finds 11-time champ Nadal across the net. Nadal will be the strong favorite, but somehow the dynamic has changed between the two players over the past couple of years, with Federer winning their past five matches, including the final of the Australian Open in 2017.
Federer knows what he has to do to have a chance. But he has to do it perfectly, or he knows what will happen.
"It's never natural against any lefty, Rafa or another lefty," Federer said. "It's just everything changes. We play 80% of the time against righties. And when we play a lefty, it's just a different match. It's an interesting match.
"I have played five guys [this tournament] that are righties, so for me, it's a complete switch-around. Just the way the ball goes out of your strings with the different spins, it's just different. So you have to get used to that quickly; you don't have much time to waste. That's why you have to be fearless, to some extent, to take on the spinny balls, the sliding balls, the kicking balls, and that's what I will do on Friday."