Nick Bollettieri: Clijsters is hot enough to make Zvonareva abandon her cool

Kim Clijsters eventually overcome her compatriot Justine Henin yesterday to earn this quarter-final against Vera Zvonareva, who won after Jelena Jankovic retired with a leg problem.

Clijsters' major strengths are her powerful, well-placed groundstrokes, hit early and with spin, and her athleticism, which underpins her great movement. Her fragility, traditionally, has been psychological, although that does not appear to be an issue for her at the moment, and it certainly was not yesterday when she came back from a set down to win in three.

As Clijsters herself described it she was trying too hard to go for her shots in that first set and got "overwhelmed" by Henin's power and shot.

"I was out there somewhere, but I'm not quite sure where," she said. "She was definitely overpowering me on every aspect of the match, I think. She was serving extremely well, returning extremely well."

But Clijsters did then find the groove and started hitting the lines and she needs more of the same today from the start: variety allied with aggression.

Zvonareva would not have been expecting such an easy day at the office but Jelena – who lived at the academy for years and has been back training recently – was struggling with her movement from the start. And as we know, Jelena is not great mentally when she falls behind.

Zvonareva has also been to the academy to use our facilities and she is very dangerous. There is a significant proviso to that statement, however; she's dangerous if she remains calm. Her biggest weakness is between the ears and if she loses her cool then she can fall to pieces.

Technically, her game is fairly simple. She bangs the heck out of the ball, and she takes it early. Her movement is wonderful, graceful. She covers the court like a gazelle. If she stays in this match mentally then she can be a threat.

Clijsters absolutely does not want to get involved in a match of bang-bang, playing Zvonareva's game, because the Russian can do that very competently. What Kim needs to do is mix it up again like she did yesterday.

It goes without saying that this is a big occasion for Clijsters in her comeback campaign. She has not played at Wimbledon since 2006 and now here she is, one victory away from a semi-final, which would equal her best-ever year at SW19.

Her ranking is No 8 in the world, which is as high as it's been since her return to the game last year, and straight-sets wins in her three matches before Henin showed she's found her touch on the surface.

This comes down to the Russian's one-dimensional but consistently strong game, against the variety and experience of Clijsters, with the key factor a psychological one.

Today's big match: Kim Clijsters v Vera Zvonareva

HOW THEY MATCH UP

Belgian.........  Nationality......... Russian

27.........  Age......... 25

Bree, Belgium.........  Residence......... Moscow

1997.........  Turned pro......... 2000

Right-handed.........  Plays......... Right-handed

5ft 9in.........  Height......... 5ft 8in

No 8.........  World ranking......... No 21

37.........  Career titles......... 10

$17.2m.........  Career prize-money......... $7m

W26 L7.........  Wimbledon record......... W15 L7

SF (twice).........  Wimbledon best.........  QF (2010)

5-0.........  Head-to-head......... 

1-8.........  Odds......... 7-1

Bollettieri's prediction: Clijsters edges it

Sharapova lost – but this performance showed her star is in the ascendant

Serena Williams had the edge over Maria Sharapova yesterday, as I thought she might, but this was not a walkover for the American champion and the difference really was in that first-set tiebreak. It swung both ways and arguably Maria could have sealed it. But she looked just a little tight and her serve broke down a bit at just the wrong time and Serena took advantage, as good champions do.

They pounce on weakness and they exploit them. That was the match for me, and once Maria had lost that first set, it was always going to be a struggle for her.

But. There's a positive but. Watch out for Sharapova as we move on into the summer because she's getting closer and closer. She's not quite ready to be battling toe to toe with the biggest guns in the Slams, but if she stays healthy and gains confidence, I think we'll see her challenging at the US Open.

As for Serena, she served very well, especially in that first set when she hit 13 aces at speeds of up to 125mph. She moved well and strongly, and perhaps most importantly of all she stayed strong in her mind in a match against someone to whom she'd lost in their only other meeting on grass – the 2004 final.

Federer not tested but he won't care Roger Federer eased into the quarter-finals by beating Jürgen Melzer but it wasn't really the kind of match where his class was needed because Melzer did not have a great day. Federer won playing well within capacity. Only a few times did we see that phenomenal change of pace from graceful, easy shot-maker to thunderous killer of points. It's been a strange tournament for the No 1 seed so far, and he'll face tougher tests ahead.

Lleyton Hewitt won't face any more tests this fortnight after falling to Novak Djokovic, and that wasn't what I expected. But Djokovic was pumped up and played very well.

Staying with the men, I was also impressed, again, with Andy Murray. He won as I expected, in straight sets, having got the early read he needed on Sam Querrey's serve, then pushed home the advantaged against the bigger, tiring man.

Beware the outsiders

The one anomalous quarter-final today is Petra Kvitova against Kaia Kanepi because one of those two is going to be in the semi-finals and on their rankings neither should have got beyond the second round. Kvitova is a big, strong Czech, age 20, 6ft tall and built solidly. She's a real powerhouse and a leftie to boot. Kanepi is older, but also strong. I wouldn't be surprised if Kvitova ends up meeting Serena Williams in the semis.

Dear Nick...

With England, the USA and Italy all out of the World Cup, we'll leave my World Cup of tennis behind! Instead, I invite your questions, either about my life in tennis or about your own game. Today's question is from Fiona Roberts, who had seen me speak at a conference and emailed to say: "You talk with great humour about having had eight wives, but in seriousness, is life as a top-level player, or indeed coach, incompatible with a settled personal life?"

Well Fiona, the simple answer is yes, it's incompatible, and at the very least, difficult. I have indeed been married eight times, and I'm blissfully happy with my wife Cindi, and our son, Gio. But there was one marriage when I was coaching Andre Agassi where my wife said 'Andre or me' and I replied 'I'll just pack and be gone'.

Several other of my marriages went west with the demands of the morning-to-night coaching needed to give proper attention to students; when Monica Seles was young, she'd stay out til nightfall hitting just one shot until it was right.

Being away for long periods is also damaging. For players it's harder to maintain relationships, definitely, and having a family on the road is tough.

Email your questions to n.bollettieri@independent.co.uk

Holy mackerel!

The heat at Wimbledon is staggering, literally. It was pushing 30 at 7pm yesterday! Look at how it's taking a physical toll on players. Novak Djokovic won but not before breathing problems. Definition of irony: rain at every single Wimbledon since 1995 (and most before), then a £100m roof is built, there's a few drops last year and none in 2010 at all quite possibly.

Win a Week at my Academy

Want a week's tennis holiday at my academy in Florida? Included in the prize is five days' top-class tuition. The prize can be for an adult wanting to shape up your game, or for a child who wants to follow in the footsteps of Agassi, Seles or Sharapova.

All you have to do is email to tell me who will win today's big match. I want a specific score line, and as a tie-breaker, a one-sentence summary of the manner in which your pick will win. All winners go into a hat, with one overall winner picked from there. Email: n.bollettieri@independent.co.uk

Yesterday's winner was Rachel O'Reilly.

If the prize is for a child, parent(s) or guardian(s) must accompany at your own expense. The winner arranges the travel.