With Pete Sampras having dropped four sets in three matches, it might seem harsh to dwell on the one and only lapse Tim Henman has had on his way to the last 16 in the Australian Open in Melbourne.

But the word lapse does not quite convey what happened to Henman against Wayne Arthurs yesterday. Collapse would be more accurate.

If it happens again against 12th seed and crowd favourite Pat Rafter when they meet tomorrow for a place in the quarter-finals Henman knows the consequences are likely to be far more dire.

Henman beat Rafter's fellow Australian Arthurs by the rather bizarre score of 6-3 6-2 0-6 6-2 in the same Rod Laver Arena where Greg Rusedski knocked out top seed Gustavo Kuerten the night before.

That third set, in which Britain's No 8 seed was so scrambled that he won a mere nine points, needed explaining afterwards before Henman could move on.

''I think it was loss of concentration - and that's never acceptable,'' said 26-year-old Henman.

''I'm a professional sportsman and it shouldn't happen. I think I got complacent because things were going so well. Suddenly he had a chance to get back into it, started playing better and I made life difficult for myself.''

With a world ranking of 82nd the big-serving Arthurs, son of a former Irish Davis Cup player, was good enough to romp through the set, but not the match.

What might have happened had he broken to 2-0 in the fourth, which he narrowly failed to do, would have been interesting to know, but in the nick of time Henman got his brain back in gear and proved himself the better man on the night.

If he wants to make progress deep into the second week, however, there can be no repeat. He knows it because should he get past Rafter it is likely to be US Open champion Marat Safin next, then either Sampras or defending champion Andre Agassi.

''The same thing should not happen. It will be a lot more intense match and the atmosphere should be brilliant,'' he added.

''I'd be the first to admit I have to go up a gear now. The matches are going to be tougher and I think there are none tougher than Rafter in Melbourne.

''His support is reminiscent of what I have at Wimbledon and I would be naive to think it's going to be tranquil out there.''

Rafter, last year's Wimbledon runner-up and winner of the US Open in 1997 and 1998, declared on the eve of the event that this could be his last attempt to become the first home winner of the title for 25 years.

At 28 he is far from old - only two years senior to Henman and younger than Sampras and Agassi - but his body has taken a hammering and he also says he wants to devote more time to charity and environmental matters.

Rafter is one of the good guys in the sport and the crowds here love him.

Even against Arthurs there was a shout of ''Come on Wayne, he's only a Pom'', but Henman must try to shut himself off from all distractions.

''On paper I might be favourite, but he has the home support and I don't think there is a clear favourite.''

History supports that. They have met four times and it is two each, with their only five-set encounter being Henman's win at Wimbledon three years ago.

If Sampras and Agassi are to have a repeat of their epic semi-final last year, this time it will come a stage earlier and for it to happen Sampras has to defeat fellow American Todd Martin and Agassi will need to see off Australian Andrew Ilie.

After starting with two four-set struggles Sampras was taken to five yesterday before beating Argentina's Juan Ignacio Chela.

Another three hours of toil, making more than nine in all, was not quite what Sampras had in mind, especially in temperatures which suddenly shot up and at one point reached a frightening 54 degrees Centigrade at court level.

Nobody found it tougher than German David Prinosil, who after losing six set points in the opening set against Agassi, fell 5-0 down in the second and retired because his pulse rate was dangerously high.

The premature end to the match means he, in stark contrast to Sampras, has played for only just over four hours so far this week - less than half the time of Sampras.

In the women's singles Lindsay Davenport started to look like the defending champion when she beat Italian Silvia Farina Elia 6-2 6-1.

After needing three sets in her first two matches Davenport was not exactly panicking, but she was relieved to produce better form.

Blocking her path to the last eight is Lleyton Hewitt's girlfriend Kim Clijsters, the 15th seed. Eighth seed Anna Kournikova was a set down and a break down to her doubles partner Barbara Schett, but survived another hurdle in her bid for a first tournament win.