The interview takes place on a ferry on the Thames shuttling Juan Martín del Potro to the O2 Arena from his hotel. His is the only name to have adorned a Grand Slam trophy other than one of the "magnificent four" of Roger Federer, Rafa Nadal (now confirmed as end-of-year world number one), Novak Djokovic and Andy Murray since 2005: the US Open in 2009. The world number five faces Djokovic in London on Thursday.
Question. People say of your forehand that it's like the five o'clock train: always on time and unstoppable.
Answer. It's my best shot. A while ago, an Argentinean mathematician who's a friend of my coach did a study of the biggest forehands on the circuit and found mine is the fastest. It's something I use when I play. I like to hit it hard, so the fans can feel the speed. I can't remember how fast the study said it was, but it was 40 km/h faster than the next one. That's a lot!
Q. They say you're a big soccer fan, and that only [Paraguay goalkeeper José Luis] Chilavert was able to calm you when you cried in the airport as a child.
A. It was my first time flying. I imagine I was crying because of that, because I was scared. I'd been in an airport before but I'd never asked for an autograph and never seen a famous person. And I bumped into Chilavert. I was there with my rackets, which were bigger than me, and I asked for an autograph, which he gave me with pleasure.
Q. Now you're so big, are you still scared of anything?
A. Because tennis is a sport that demands maturity, you always have to think you're older than you are. I'm not afraid of airports anymore and I'm not afraid to wander around any city in the world because I've been doing it since I was young. But I'm only 25 and can have the same fears as anyone. I have vertigo. I wouldn't get on a rollercoaster in a million years.
In a five-hour match against Nadal or Djokovic you're not going to win by waiting for mistakes"
Q. Do you still have your Boca Juniors teddy bear? Do you travel with it?
A. I don't travel with the bear, but I have it in my house in Tandil, in my bed, waiting for me when I go home. Imagine, 25 years old, nearly two meters tall and carrying around a teddy bear! It wouldn't look very good...
Q. This year you've beaten Nadal, Djokovic, Ferrer, Murray and Federer.
A. It's difficult to do. I saw in the paper that I'm the only player to have managed it, which shows how good those at the top are and how difficult it is to beat them. It was one of my aims this season: to be able to compete against the best. You have to have more than tennis: a good mentality, to stay in shape... I feel like I'm in an era that if it isn't the best of all time, is definitely one of the best. To be part of it, to compete against these guys and even beat them, makes me very happy.
Q. Your style is wham and bam. Do you need a Plan B?
A. The hard thing is to find your own style. When it is implemented and comes naturally, you have to stay on that path. Of all the options someone could present me with, I think the one that suits me best is the one I use. Attack, hit the ball hard and try not to run around too much. That's how I can beat the best players. In a five-hour match against Nadal or Djokovic you're not going to win by waiting for them to make mistakes. I keep working to be more aggressive, to hit the ball harder. And to know when to go for a shot and when to come to the net. That's my Plan B.
Q. Opponents try to bring you into the middle of the court with low balls.
A. Some try and I'm able to overpower them. The difference is the players who are very good at it make me commit errors. It's hard for me to bend my legs, because of my build. If I fall into their strategy, they know better than me. I have to overcome them with power. Nadal's topspin, for example, kicks up high for most players but for me it's a good height to attack.
Q. You dropped to 485 in the world after a wrist injury, and Nadal, who was out for seven months, is back winning. What do you have in common?
A. Desire, the challenge to come back. I couldn't play for almost a year. The worst fear I had was that I wouldn't be able to return. It was a big setback, a personal and professional test. Winning or losing, I'm never going to feel like the best or the worst player. Sometimes, the person has to pick the player back up.