It has been quite a week for Australian umpires. Last Saturday Ross Emerson called the Sri Lankan off-spinner Muttiah Muralith aran for throwing - "The Ball That Stopped The Summer", as it was dubbed - and yesterday at the Australian Open, Melbourne's Denis Overberg docked Venus Williams a crucial quarter-final point when, for the second time in the same game, showers of beads spilled from her hair on to the Centre Court.

On a wet first week of Wimbledon two years ago, when there was nothing much else to do, there was considerable speculation about what might happen if the beads of either Venus or her younger sister Serena ever cascaded on to the court.

The current rule is that, if any item of clothing falls to the ground, the umpire may initially call a let, allowing the point to be replayed. If it happens again, the offender may be penalised a point.

In last year's US Open final Lindsay Davenport's cap fell off and a let was played. "Since then I've always made sure it was on good and tight," said Davenport yesterday, having beaten Williams 6-4, 6-0 to reach the semi-finals.

Davenport may have expected to expend beads of sweat against her turbo-hitting fellow American; even resorted to prayer beads if matters had become particularly tough. But not this.

"I don't think it was a very fair call," complained Williams, who pointedly refused to shake hands with Overberg when the match finished. She had thought herself unsinkable before this match but like the Titanic she was scuttled by a berg.

The initial incident occurred at the beginning of the third game of the second set, which Davenport was leading 2-0. As Williams served, a whole string of white beads, which are threaded to her hair, pinged on to the court, and a let was called in mid-rally as the umpire spotted the offending objects.

"You could hear them," said Davenport, "but it wasn't a total distraction, just a little bit annoying."

After the let was called Williams was warned that any repeat would cost her a point. That is exactly what happened in the next point but one after a mishit volley by Williams had given Davenport a break-point at 30-40. Williams was 3-0 down.

After a lengthy argument with the umpire, Williams called for the tournament referee Peter Bellenger and there followed a further protracted discussion. "I guess the rule was never written for beads," said Williams, although she admitted that she lost the match because "I didn't play so well".

"I think Lindsay played quite nicely," she said, like a maiden aunt talking about a not-much-loved cousin. And will she and Serena now forsake their beaded hair? "Never."

Davenport's metamorphosis from a somewhat dumpy slugger with a dodgy temperament into the best player in women's tennis has been extraordinary. Prior to her triumph in last year's US Open, where she beat Martina Hingis, the 22-year-old Californian had never reached a Grand Slam final. Diligent training, including regular sprints, shed a stone and gave her supreme confidence in her ability. She remains cheerfully unassuming off court but, once on it, appears unbeatable.

For the first few games yesterday she carefully assessed the Williams threat and then launched on to the attack. The two matched each other for power but Davenport, the number one seed, was always the more controlled.

Having been broken in her second service game Williams, seeded number five, fought back as Davenport served for the first set at 5-4. Four times Williams threatened to level but Davenport did not lose a deuce game throughout the match and ended a comfortable winner.

She next plays the unseeded 19-year-old Frenchwoman Amelie Mauresmo who in yesterday's other quarter-final defeated Belgium's Dominique van Roost, the 11th seed, 6-3, 7-6.

Mauresmo, a former Wimbledon junior champion, is ranked number 29 but possesses a wicked serve and a fine all-court game. She won her only previous meeting with Davenport 6-2, 6-4 in Berlin last year, although that was on clay and before the American's transformation.

In the two men's quarter-finals Sweden's Thomas Enqvist defeated Switzerland's Marc Rosset, the third-round conqueror of Tim Henman, 6-3, 6-3, 6-4 and will now play Ecuador's Nicolas Lapentti, who beat Slovakia's Karol Kucera, the number seven seed, 7-6, 6-7, 6-2, 0-6, 8-6.

Lapentti, ranked 91, has never previously progressed beyond the second round of any Grand Slam although the 22-year-old was an outstanding junior. Given the colossal upsets in the men's tournament so far, nobody would be altogether surprised if he emulated the Brazilian Gustavo Kuerten's unexpected French Open victory in 1997.

Men's Singles - Quarter-finals (prefix numbers denotes seeding): T Enqvist (Swe) bt M Rosset (Swi) 6-3 6-4 6-4, N Lapentti (Ecu) bt (7) K Kucera (Svk) 7-6 (7-4) 6-7 (6-8) 6-2 0-6 8-6.

Women's Singles - Quarter-finals: A Mauresmo (Fra) bt (11) D Van Roost (Bel) 6-3 76 (7-3), (1) L Davenport (USA) bt (5) V Williams (USA) 6-4 6-0.