Nick Bollettieri's Wimbledon Files: My boy Ryan Harrison has fighting attitude to take on Novak Djokovic

You are 20 years old, you have played three matches at Wimbledon, you have never won a senior title and over your young career have lost more single matches than you have won. So here's the question for Ryan Harrison today: how do you beat the best tennis player in the world, the defending champion, a guy who belongs among the greats, a guy who does not possess an obvious weakness on the tennis court?

I spoke to Ryan yesterday and he said, "Nick, I will be ready mentally for this match." You can be assured that – the mentality – is going to be so, so important if he is to challenge Djokovic out there today. This is a battle of the mind.

Here's what I say to my guys: do everything in life with purpose, whether on the sports field or off. Harrison knows this because he has heard me say it at the IMG Bollettieri Academy where he trains and he is someone who has a purpose. I know him well. He comes from a real tennis family, his father, Pat, played at college, his sister is a good player – she will get a scholarship to college – and his younger brother, Christian, 18, has what it takes to follow his big bro into the pro game.

His father deserves a lot of credit for the player Ryan is. So here's the story: off court he is a sensitive, low-speaking, nice guy. Get him on that court and he changes: he will go head-to-head, toe-to-toe with anyone, fight tooth and nail. He becomes a guy pumped full of emotion. That is going to be key to his success over the next two to three years, because he can be good if he can get that right,

It's not a question of his playing skills because this boy has all the tools for success. He has a huge forehand, an excellent two-handed backhand, a super slice, a big serve that ranges from 120-130mph and a penetrating second serve, and he is not afraid to come in and volley either. He moves and anticipates extremely well – physically he's got it too, well built and in good shape.

So far so good, but then take a look across the net. Holy cow! Novak Djokovic is simply one of the best. Look at his record, it's all there: ranked No 1 in the world, above players as good as Roger Federer and Rafa Nadal, won four of the last six Slams. You can talk all day long about how to beat him but the problem is that this guy does not have an outstanding weakness. There isn't one; it's all there, backhand, forehand, serve – effective second serve too. He's got great lower body strength, covers the court like the athlete he is. The volley's there, the drop shot, the slice – and since they sorted his diet out a couple of years ago, his fitness is outstanding, too.

Harrison has the type of game, a forcing game, that means he is not afraid to duel it out with you. He can strike that big forehand – and man, it's huge – from anywhere on the court. That's a weapon, and one he's got to use – he must not take a back seat. He has the guts to say, "If you want to hit a big forehand at me fine, I'll hit it right back at you."

His serve equals his opponents and his stats from his first round win were good – 70 per cent of his first serves were in, at speeds of up to 130mph, which is marginally quicker than Djokovic.

But leave aside all the tennis skills, this will be a mind game. I expect a heck of a match, four sets or more, and it will not be easy for Djokovic. Of course Djokovic is a big favourite, but if Harrison can stay tough up top – not let his mind slip for one minute under the pressure that will come from the Serb – then he can make it tough on the court for Djokovic.

Today's big match: Novak Djokovic v Ryan Harrison

How they match up

Serbian Nationality American

25 Age 20

Monte Carlo Residence Austin, Texas

Right-handed Plays Right-handed

6ft 2in Height 6ft

1 World ranking 48

30 Career titles 0

$37.6m Career prize-money $838,070

27-6 Wimbledon record 2-1

Winner, 2011 Wimbledon best 2R, 2011 & 12

1 Head-to-head 0

1-50 Odds 12-1

Bollettieri's prediction Djokovic in four sets

Thoughts for the day

1. Let's see how tough Janet is

So there I was yesterday, minding my own business, watching a bit of tennis when I get a call from the BBC. They've got Janet Street-Porter and she's been on the radio saying she had read Andre Agassi's book and thought I was too strict and unfair on Andre when I coached him.

"Do you want to talk to her?" they said. "Sure," I said. Boy that was fun debating with her, she's one tough lady. And you know how it ended? I said to her "Janet, come to Florida – I want you to come to camp and find out just how tough it is for yourself."

So I've offered her a week's coaching at the IMG Bollettieri. It's never too late to work on your game Janet. We're looking forward to seeing you in Florida.

2. Finally... a British winner

Speaking of home, I'm lucky to be over here and not only to be at Wimbledon. There's a storm whipping up the coast in Florida so for once the British weather is the winner.

Coaching report: S Williams V Strycova & Kvitova v Amanmuradova

It was all about business out there and Serena got the job done. That's the first round for you, get it done and move on. She actually looked in pretty good form, straight sets, getting that first-serve percentage pushing 70 – her game seems in good working order.

I'm sure she had Venus in the back of her mind a little – it's tough to see your sister go out so quick – so she will have been pleased to come through with no problems. Serena will be a factor in this tournament. I will be surprised if she does not go deep into the second week.

Right now as they are getting older – Serena is 30 – I'm sure their physical condition is important. Venus is certainly going through some difficult times but yesterday she announced she has no thought of retiring. She wants to play the game, and it's great to see that the Williams sisters will be playing doubles together for the US at the Olympics.

Serena plays a little differently to her sister, she is more comfortable at the baseline, but it is much too early to start measuring her against Maria Sharapova and the rest.

Petra Kvitova started off slowly but she kept playing her game. She looked to hit winners, they didn't go her way and she dropped down 4-1 but that did not put her off – she stuck to what she knows best and it came about.

Watch out for Kvitova again. She is such a dangerous player because she goes for those winners relentlessly and has a good serve too. But don't forget how different the conditions get in the second week as the courts start to get bare. That can change things dramatically.