Nick Bollettieri's Wimbledon Files: Del Potro has the power, Nishikori the shots – boy, it will be some tie

Nishikori’s secret is his footwork and balance – his return of serve is superb

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Juan Martin del Potro is a mighty big boy and comes equipped with some mighty big weapons to match. The biggest is his serve – man, it's supersonic. The Argentine is capable of blowing opponents away but what is so appealing about this contest is that on the other side of the net is a young magician, Kei Nishikori. It will be a complete contrast in styles and that raises the prospect of a mighty match-up.

If you look at all the players in this tournament – and there are some huge, huge names out there – nobody is better in the creation of shots than Nishikori. The secret is his footwork and great balance – he gets around the court quickly and takes up position early. He's dangerous because the opponent cannot anticipate what he's going to do.

What about his game? Keep an eye out for his backhand – he likes to leap off his feet to hit it two-handed. His forehand is excellent, clean and penetrating and he has a short backswing. His serve has improved a great deal because he is reaching up for the ball and using his legs a lot more, while his return of serve is superb.

That will be important in this match. He can change the pace with a delicate slice and drop shot and he can also hit low balls with an underspin forehand and that may help him against Del Potro.

Nishikori has come a long way since he arrived at the IMG Bollettieri academy when he was 13. And I believe he is going to go further. I'm going to go out on a limb here, out to where the cherries are hanging, and predict that Nishikori will break into the world's top 10 by the year's end. He had a poor summer last year and so doesn't have many points to defend; he reached the last eight in Australia and this is already his best on the grass.

Nine years ago when he arrived in Florida – where he still lives – it was his first time outside Japan. He could not speak English real well, was homesick and faced with strange food. He was so shy. It took about three years for him to settle and get used to our American ways, but holy cow has he settled now.

He has an outstanding coach in Dante Bottini. What Bottini does is look to make everything positive. They spend hour after hour together and there is never any shouting. What Bottini has learnt is that when you have a shotmaker coaches should not overtalk, not complicate things. You have to be careful how you deal with shotmakers – don't screw them up. Sure, you add something here or there, but do it with extreme caution. Shotmakers are unusual – if you tinker too much you can take away that creativity, then you stymie their career.

Nishikori suits grass, he moves well and can pick up low balls. He's able to get balls hit behind him and he's tremendous in recovering short balls forward. He cannot get into cross-court rallies and try, badda-bang, to out-hit the big boy. He will not come out a winner that way. He must hold his serve – you only need to break one time – but he must, must hold and then look to move the big boy around the court.

Del Potro has done well to return to the top 10 after a wrist injury. That is a tough injury to come back from – a bad wrist can mess up your career, but he has all his power back. And watch out for the way he hits on the backhand. It's so dangerous because he comes inside the court and catches it above his shoulder, which puts more pressure on the opponent.

What's important here is that Nishikori does not get discouraged. Some bombs are coming his way. He has to find a way of dealing with them but, as we saw on Centre on Thursday night, nothing is certain in sport. That's why we love it.

Today's big match: Juan Martin del Potro v Kei Nishikori

How they match up

Argentinian Nationality Japanese

23 Age 22

Tandil, Argentina Residence Florida, US

Right-handed Plays Right-handed

6ft 6in Height 5ft 10in

9 World ranking 20

11 Career titles 1

$9.1m Career prize-money $1.7m

8-4 Wimbledon record 2-3

4r 2011 Wimbledon best 3r 2012

2 Head-to-head 0

2-7 Odds 11-4

Bollettieri's prediction Del Potro in four sets

Thoughts for the day

1. Match pint

What a day yesterday. I had to recover from being introduced to Guinness the night before. Holy of holiest cows, what sort of stuff is that? I was watching the soccer in a pub, the Italian in me coming out with every ball kicked, when this guy recognised me and asked to buy me a drink. I couldn't say no. It kept me up all night – what's in that stuff? That's the end for me and Guinness.

2. I'm in with the in-crowd

I had a ball with Richard Bacon at lunchtime, going out on the Hill and doing a Q&A with the fans. Man, I love the Wimbledon audience.

3. Been through some stormy times

As I set out in the rain yesterday morning, a thought struck me. You know – the London weather changes more often than I change wives.

Coaching Report: Novak Djokovic v Radek Stepanek & Sabine Lisicki v Sloane Stephens

It's looking good for athletic Djokovic

When the stoic Radek Stepanek took that first set there was the scent of another upset under the roof on Centre Court.

There were signs that Novak Djokovic was getting frustrated – things weren't going his way, his game was a little off.

But this is man who knows how to keep his emotions in check. He is also one hell of an athlete and his athleticism helps grind an opponent down. At 33, Stepanek may be the oldest man in the field – hey, what's age matter? – but he can play on his day.

Djokovic, though, never gave him a chance to build on that first set.

His game began to click, that short backswing, speed, all-round athleticism.

He breaks you down stroke by stroke, serve by serve, and by the end of what turned into a straightforward win all was in was in working order. Looking good Novak.

Now Sloane Stephens is somebody worth keeping an eye out for over the next couple of years.

She is only 19 – and there are not many teenagers making a mark in the women's game at the moment – and has plenty of ability.

Stephens is an athlete too but what she needs to do is to get mentally stronger, learn how to deal with adversity on that court.

There were times yesterday in her defeat against Sabine Lisicki when she sent out too many negative signals and that just feeds into her opponent's hands.