When Juan Martin del Potro was leading 6-3 2-2 in his semifinals match against Roger Federer in Shanghai, it seemed the match was on his side. Then in the long fifth game Federer break. Do you think that was crucial to change the momentum of this match? 'Well, for me it was', the 19-time Grand Slam Champion said in press conference.

'Clearly getting the break and then holding, I mean, it's always key in tennis. So I'm happy I was able to do it, especially with all the twists and turns and, you know, blink at the wrong time, you know, he might hold the game and then you don't know what's going to happen next or I have to go through the breaker maybe, or because I'm with my back against the wall I might play a poorer game later on in the set.

I played a very clean second set. I had many more chances on the return. Hardly dropped points on my own serve. Probably was a bit better in that second set. And then it's just important to somehow get it done. Sometimes you need the help of your opponent, and sometimes it needs to work out the way the point plays out.

Yeah, it was good energy out there on the court today, and I really tried to push myself after playing a bit of a subdued maybe first set, but Juan Martin didn't allow me to play so much in that first set.' 38th match with Rafa.

Talk a little bit about - that's a lot of matches, and they have been very competitive and whatever - what that's meant in your career. 'Ones to look back on, because most of those matches -- I'm not sure what the stat is, but maybe half of them maybe in finals.

That's why I think the rivalry is so special. The way we both play, we play so very different from one another. Also, the attitude, the way we go through our lives, you know, it's all very different in some ways. Yeah, we have a similar mindset in the big moments.

I came to realize that when we played doubles. There is no sense of urgency or panic, I don't want to say ever, but, you know, you could tell we have been there many, many times before. He's a great champ, and I enjoy playing against him, even though the head-to-head is maybe not in my favor.

I think he's definitely one of the guys that make me a better player. I don't want to thank him for that, but he made me maybe rework my game and go back to the practice courts and think about what I could change maybe to become a better player.

I think for that I'm happy about the losses I took, you know. Took them on the chin and kept moving forward. It's nice at this late stage of the career that we still have these matches going on.' Juan Martin picked you as the likely winner of tomorrow's final, largely because of the speed of the court.

Can you talk a little about playing on this court and how it helps your game. 'Margins are small. On fast courts it's always, like I explained before about the break points, it's got to sort of match up, you know, with -- is Juan Martin going to serve so well on the big point that you can maybe almost do nothing about, or is he going to use the combo of the serve and forehands so perfectly that you just almost cannot come through, you know, even if you create so many chances.

And maybe tomorrow is the same thing. There is only going to be a few chances for either player, and sometimes it's just who blinks, you know, at the wrong time. So it makes it always a close match on faster courts. But for me it's good.

You know, the slice stays lower. I naturally play on the baseline. Maybe Rafa doesn't have that many opportunities to go way, way back to return, even though he can also do it on hard courts and he's the best ever to return from way back there.

So he almost has to play up on the baseline, but he's been doing that almost perfectly here this week, you know. He's maybe even surprised some of his opponents to play this good on the baseline and outplayed those guys.

So, I mean, look, he's a great player on hard courts. On fast, as well. He wouldn't have won Wimbledon otherwise. It's going to be a tough one for me. I mean, I hope, of course, the service might help me a little bit.

That would be nice, anyways.' The last time you played Rafa in Shanghai is 2007. Compared to 10 years ago, how has your relationship with Rafa changed and evolved? 'He looks different (smiling). He's not wearing the croppy pants anymore and sleeveless shirts and stuff.

The relationship? We were cool way back when, you know. I think we always got along very well. Always had a lot of respect for one another. He used to be more quiet and calmer and more shy way back when just because I had been on tour for almost 10 years at the time, and he was going through the motions with decision-making and all that stuff, especially at the ATP level that whatever Roger thinks, I'm his opinion, too.

Then as time went by, you know, he had his own opinion, which I thought was great. His character grew and became more confident. In the process, our relationship became bigger, I guess, you know, because we had to -- we had some arguments, we had some disagreements, but for the most part, it was always good, you know, and very nice.

I think especially the last few years have been a pleasure for us. You know, especially being injured, for me, as well, seeing what he had to go through. I could never really relate to injured players, to be quite honest, because I never really was that hurt like he was.

I think the last year was a good reality check for me to maybe understand what he was going through so often. And then of course, you know, I was always happy for him, especially down the stretch of his career, that he kept on winning and proved people wrong, like I was trying to do the same.

And then we went to open the academy almost today on the day last year, which I know is very personal to him and very important. Especially with Laver Cup now, as well, the last year. It's been great for both of us. I'm happy to call him a friend today.'