THERE is no greater fall in women's Grand Slam tennis than that of Steffi Graf. For more than a decade, save for one wretchedly gloomy and dank summer's day at Wimbledon in 1994, the German has never turned up in Melbourne, London, Paris, or New York without making it through to the second week. And more often than not she has reached the final.

But yesterday, on an afternoon when the heat was so intense on the centre court that it seemed as if 100,000 oven doors had been opened simultaneously, Graf lost 6-2, 7-5 to Amanda Coetzer of South Africa, the number 12 seed.

Graf, who had been feeling unwell prior to the match because of an infected toe, which was treated on Saturday, was too exhausted to talk afterwards, and a written statement said that the temperatures had exacerbated her condition, resulting in "cheat illness".

But there bad been clear indications in her second and third round matches here that all was not perfectly well, yet so used has the tennis world become to stories of Graf's injuries that nobody paid too much attention and expected, as usual, that everything would be right on the night.

Graf's back problem, in particular, is a perennial topic, yet she has missed only three of the majors since 1988, all of them here, including the two previous years. But the possibility of her father, Peter, being jailed for tax fraud later this week was thought by many to be the real reason for her indifferent form.

There were few indications during the early part of the match that there was anything physically wrong with Graf, although in the second set she frequently moved towards the back of the court in between points in order to gain what little shade there was.

More starkly obvious was the huge number of errors the German was making both on her backhand, the weaker shot, and her usually omnipotent forehand. Here were echoes of her quarter-final loss against Martina Hingis at Rome last year, when her father's problems were again at the forefront of her mind.

Coetzer, who reached her one Grand Slam semi-final here last year, eventually losing to another German, Anke Huber, displayed not the least compunction in trading forehands with Graf and frequently came off the better.

From the moment Graf lost her first service game a murmur of expectancy swirled around an otherwise stiffingly still arena, and when Coetzer took a 4-0 lead inside 12 minutes the murmur turned to animated babble.

Yet even after Graf had lost the" opening set 6-2 there seemed no real reason to suppose that the top seed would not roar back, as she had done so often before in early round matches. All the players know that the German occasionally displays initial uncertainty, but few, particularly at Grand Slam level, ever have the opportunity to press home such an advantage.

Indeed, since Graf won the first of her 21 Grand Slams at Roland Garros in 1987, she has lost to only eight players at this exalted level, the worst defeat being that first round" loss at Wimbledon against Lori McNeil of the US.

This fourth round defeat by Coetzer, currently ranked 26th, is thus the second biggest shock, although when Graf held her serve to love at the beginning of the second set, and then broke the South African twice for a 4-0 lead, it appeared that her deficiencies in the first set were about to be banished in typical style.

In the post-match statement Graf generously praised Coetzer, adding: "I tried as hard as I could. I just didn't have the energy with the heat." Boris Becker had expressed, similar problems after the reigning champion lost on the opening day of the tournament.

On Saturday, the number two seed, Arantxa Sanchez Vicario, also lost, going down to the little-known Belgian Dominique van Roost 1-6, 6-4, 8-6, and there were further upsets yesterday with the disappearance of the number three seed, Conchita Martinez, Huber the number five, and Lindsay Davenport, the number seven, thus paving the way for a first Grand Slam title for the 16-year-old Martina Hingis, seeded four.

Martinez fell after taking the first set 6-2 against Sabine Appelmans of Belgium, while Huber lost in straight sets to Mary Pierce, the 1995 champion here, who has been playing with increasing confidence and slightly diminished affectation.

In the men's fourth round matches there were wins for Michael Chang, Carlos Moya, Felix Mantilla, and the very dangerous Marcello Rios, who now plays Chang in the quarter-finals.