TENNIS:The best coaches in the world are rendered impotent if their players refuse to listen to their advice, and although Brad Gilbert did all in his power to change Andy Roddick's game he failed and they split. It took Jimmy Connors, an eight-times grand slam champion, to shake up Roddick's game and his five-set fourth-round victory over Croatia's Mario Ancic duly kept the much improved American on course to meet Roger Federer in the semi-finals of the Australian Open.

Andy Murray does not have the raw power of Roddick, though he can already hit a mean serve and forehand. However, he has far more natural talent - as much as anybody in men's tennis except for Federer - and when Gilbert became his coach last year there was no need for root and branch change. The American's major influence has been to get the teenager to train properly and diligently.

This is what he hopes will show when Murray meets Spain's Rafael Nadal, the world number two, today in the Rod Laver arena, the prize being Murray's first slam quarter-final.

It is no secret that Murray, in his younger days, was always shy of pushing his body to the limits on the practice courts and in the gym. Now the dime has dropped, as it had to.

Murray's talent was always enough to take him to the top as a junior and ensure his fledgling professional career went reasonably smoothly, but now the hard graft has begun.

Federer and Roddick are big, heavy-boned men, and Murray is intent on filling out his upper body and strengthening his legs. He already has a huge advantage over Tim Henman who, for all his assiduous training, is essentially a lightweight in physical terms and never really had any big weapons.

Mark Grabow, who works with the Golden State Warriors basketball team, based in Gilbert's home town of Oakland, has trained a variety of athletes and has had such an influence on Murray that the youngster is keen to get back to California after the Australian Open in order to further test his physical progress.

Murray's third-round victory against Argentina's Juan Ignacio Chela, who beat him in the first round here last year, was compulsive if one-sided. Chela has a similar game to Murray, although much plainer. Apart from the opening few games in the first set, the Argentinian was left for dead. He is one of the game's great slow walkers, taking a seeming age to get from his chair to the baseline, although once in action he can be surprisingly fleet. He needed to be, as Murray worked him around the court at will. It was his best performance here, and one of his most complete at any of the slams.

It took Henman five years to reach the fourth round of the Australian Open; Murray has done it in two. He may have been a little fortunate not to have played on one of the less sheltered courts in the middle of the day, as Henman so often had to do, but the security of Murray's ground strokes make it so much easier for him to cope when the wind gets up, as it does so often here.

His win over Chela saw him reach the last 16 of a major for the third successive time, a true indication of his progress in the last year.

Murray is one of a clutch of young players gathering to challenge Federer's dominance. The youngest is Serbia's Novak Djokovic, who is just seven days Murray's junior.

He has vowed to become the world number one, though all such aspirations were put into perspective yesterday when Federer, chasing his 10th slam title here, crushed the 19-year-old 6-2, 7-5, 6-3. It was a masterclass.

Federer next faces Spain's Tommy Robredo, who slipped almost unnoticed into the top 10 last year under the shadow of Nadal.

Robredo has continued to confound his numerous critics by reaching the last eight, yesterday defeating France's hugely gifted Richard Gasquet 6-4, 6-2, 3-6, 6-4.

The other quarter-final in the top half of the draw will be between Roddick and his fellow American, Mardy Fish.

"We've gotten into each other's faces numerous times, especially when we were younger," said Roddick after yesterday's 6-3, 3-6, 6-1, 5-7, 6-4 win over Ancic.

If Fish, now number 42, wins then Roddick would be mortified, for his eyes are set firmly on that Federer semi-final, and the chance of only his second victory over the Swiss in what would be their 14th meeting.

Guardian Service