If a 6ft 10in Croat is doing a grotesque cowboy impression on centre court this afternoon it will be very bad news for Roger Federer and very good news for Andy Murray.

If a 6ft 10in Croat is doing a grotesque cowboy impression on centre court this afternoon it will be very bad news for Roger Federer and very good news for Andy Murray.

That is the bizarre celebration dance which has greeted every Ivo Karlovic win on his brutal route to the quarter-finals, and another glimpse of it today would mean the men's singles event had suddenly become wide open indeed. It will be very much a case of beauty and the beast when the 30-year-old from Zagreb takes on the five-time champion and world No.2.

Karlovic - the tallest player ever to play on the ATP tour - has served 137 aces in his four matches so far, taking him beyond Jo-Wilfried Tsonga and Fernando Verdasco, the ninth and seventh seeds respectively.

His top serve of 141mph is the quickest in the competition, and it is one which has yet to be broken. Even Federer cannot match that.

It all means much will be decided in the margins, just as it has in the previous nine meetings between the pair. And although Karlovic has been getting plenty of tie-break practice, no-one plays better in the big points than Federer. The Swiss leads the head-to-head 8-1, having nicked nine of the 12 tie breaks the two have contested.

"The reason why he was No.1 and also why he's maybe the best player ever is because in the tight situations he can play his best tennis," Karlovic said. "In tie breaks I just try to relax myself, focus on my serve and try to concentrate on actually trying to realise what he's most likely going to do. That's it."

Karlovic is capable of occasional brilliance from the baseline but for the most part he is a throwback to an earlier era. "I don't know if it is sad the way the game has changed but I grew up watching serve and volleyers like Boris Becker, Stefan Edberg, Goran Ivanisevic and Pete Sampras. Back then it was more of a variety."

But then, in some ways, the entire quarter-final draw has echoes of a bygone age, each tie possessing its own share of intrigue. On Court No.1, Tommy Haas will face world No.3 Novak Djokovic, the precursor to a headline act which sees two former world No.1s, Lleyton Hewitt and Andy Roddick, reliving former glories.

Australian Hewitt had become less of a force but, after recovering from hip surgery, he has looked close to his best in recent days. Two-time finalist Roddick is also enjoying a revival after working hard on his fitness and, after beating Hewitt at Queen's, the sixth seed is looking forward to it.

"I have loads of respect for Lleyton, what he's been able to accomplish," said Roddick, who has won the last four meetings. "Everyone knows he's capable of playing very, very, very well on this surface. I've seen him play too much good tennis to have let him drift too far from consciousness as far as the top guys go. It's a fight, everything is a fight against him. Lleyton's not going to give you anything.

"A lot of guys you can get on top of, you can get on top of their game, you can look for holes in it. But Lleyton doesn't really have a lot of holes."

Hewitt, meanwhile, is determined to reverse the result from Queen's, where Roddick triumphed in two tie-breaks. "At Queen's there was only one or two points in it," the 2002 champion said. "You know you're going to get aced out there. You've got to weather the storm and take those small chances when you get the opportunity."

The same goes for Federer against Karlovic. Unless, that is, he wants to see that infamous "victory dance" again.