Nick Bollettieri's Wimbledon Files: Victoria Azarenka plays poker but Serena Williams holds all the aces

Serena's serve was awesome. No woman could have answered it

What more can you say about Serena? What she has done, what she has come back from, is an inspiration and she looks as if she is coming right back on to her game on court, too. Man, she is sparking again and she's going to be a hard woman to stop.

She knows it too. I've told Serena in the past: "Keep your shoulders up, don't give your opponent any idea that you think she may beat you." Against Petra Kvitova her shoulders never dropped, she always looked confident of winning. I really liked her positive attitude.

Today she is up against a master of presenting a winning face. I was watching poker the other night and Victoria Azarenka is like a poker player. She doesn't change expression. She just stares you down, as if daring you to throw in too many chips.

Serena has won seven out of the eight matches between the girls, including the last five, and she beat the Belarusian 6-1, 6-3 in Madrid the only time they met this year. But that doesn't mean much today. I always say that when you come to Wimbledon you have to throw out those records and Azarenka will have binned them at the locker-room door.

This is her second successive Wimbledon semi-final and she has breezed into it. While Serena has had tough games against Jie Zheng and Yaroslava Shvedova her opponent has not dropped a set in five matches. The quarter-final was the first time she had even been pushed to a tie-break.

Azarenka is young, 22, she likes to hit – she has a powerful, powerful forehand – and she is not afraid to come to the net. Where she has improved is that she is much better defensively. If you want to be the best in the world, offensive power is not enough. You need to be able to change the pace, to give yourself time to get into position to return. When she is in trouble she hits deep down the centre to neutralise the angle of her opponents and uses her footwork – which is good for a big girl – to get back in position. She also plays the big points well. She stands close to the baseline and hits powerful groundstrokes from there. That's similar to Serena. If you can pick up the ball quickly you can catch your opponent out of position and win the point.

I'm hoping to see Serena counter that by mixing it up a little. She has powerful groundstrokes but hits with very little spin. Every once in a while I tell her: "Don't be afraid to throw in a high ball deeper, especially if your opponent is hitting flat." Serena has got to be able to do that.

Even more important will be maintaining her serve. Serena has the advantage in that department. Her serving against Kvitova was awesome. No woman could have had an answer to that. Holy cow, she was hitting speeds of up to 120mph!

She will need to maintain that form because Azarenka has a real powerful service return. That's a big, big asset because it puts pressure on the server, who will then often ease up on the first serve to make sure they get it in, or overhit the second. There's one way to avoid that: boom down an ace. Today, aces will be Serena's friend.

It will not be easy, but I've got to tip Serena to reach her 18th Grand Slam final.

Today's big match: Serena williams v Victoria Azarenka

How they match up

US Nationality Belarus

30 Age 22

Florida Residence Monte Carlo

Right Plays Right

5ft 9in Height 6ft

6 World ranking 2

41 Career titles 12

$36m Career prize-money $13.5m

65-8 Wimbledon record 20-6

Winner x 4 Wimbledon best Semi 2011

7 Head-to-head 1

4-7 Odds 11-8

Bollettieri's prediction Williams in three sets.

Coaching Report: Novak Djokovic v Florian Mayer

Florian Mayer is a magician. You don't know what he is going to do. He looks like a windmill. He plays this two-handed slice which dances on the other side and he's clever how he follows to the net. Opponents get frustrated and can over-hit. Novak Djokovic dealt with this by coming up with the big serves on the big points. That's the mark of a Grand Slam champion.

Djokovic now plays Roger Federer, who was on and off court before you could say "holy cow". Bam, bam, bam. Three sets. I thought it was good of Roger not to keep Prince William and his wife waiting to see Andy Murray, but Mikhail Youzhny's single-handed back-hand made it easy. It's going to be a great semi-final between Federer and Djokovic. Who's going to win? I'll tell you tomorrow.

Any questions for me about Wimbledon, or anything about tennis? Drop me an email at sport@independent.co.uk and I'll reply to the most interesting the next day. Best, Nick