Those who believe Roger Federer to be the greatest grass-court player ever received more evidence for their argument on Wednesday when the three-times Wimbledon champion eased through his quarter-final.

His opponent Mario Ancic of Croatia played superbly, varying his style between powerful serve-and-volleying and solid baseline play. But it simply was not enough to hold the Swiss at bay. Despite rain breaks and a court invasion by fathers' rights protesters - one of them dressed as a young John McEnroe - Federer was able to maintain concentration and squash Ancic three sets to love, 6-4 6-4 6-4.

When play started on Centre Court, thunder clouds were looming above south-west London. Only four games were completed, all going with serve, before the services of the court coverers were called upon.

Once back on court, Federer then required only three points to break his opponent. He quickly proceeded to steamroller his way through the rest of the match, thwarting every increasingly desperate attempt Ancic made to resist him.

The 22-year-old from Split, who learnt much of his court craft from compatriot Goran Ivanisevic, was the last man to beat Federer at Wimbledon. That was in 2002, however, before the champion had fully asserted his All England Club dominance. Nowadays Federer has elevated his grass-court matches to an entirely different level. There comes a stage halfway through every one of them when his opponent's shoulders start to droop and his facial expression gradually switches from hope to exasperation.

The latter emotion began to manifest itself at the beginning of the second set, when Federer had whipped yet another of his angled forehands past the flailing Ancic. Every time Ancic produced a fine shot, the 24-year-old Federer would trump it with something even more brilliant. Deep volleys were met with unreturnable passing shots; dying drop-shots were inevitably retrieved. Players less mentally strong than Ancic would have thrown up their arms in despair.

Three-love down in the third set, the Croat needed both luck and immense skill to do it, but finally broke his opponent's serve - only the second time this has happened during the tournament. It was a teasing glimmer of hope that served only to delay Federer's inevitable win by a few minutes.