WHEN the north wind doth blow during the summer months in this city then all sensible folk dive for the air conditioning and refuse to come out Brevity is of the essence for any outdoor activity not involving water and the last thing any tennis player wished to do yesterday was get involved in a five set marathon.

Yet this is exactly what happened to both Pete Sampras and Goran Ivanisevic. By midday, when even Englishmen and mad dogs had run for cover, the conditions were virtually unbearable, rising to 42 degrees Celsius in the shade of which there was precious little.

It is at such times that shocks can and do occur and both Sampras and Ivanisevic were forced to drag themselves from the brink of fourth round defeats against unfancied opposition to reach the quarter finals of the Australian Open.

At the end of his 4-6, 6-2, 6-7, 6-3, 6-3 win over Norway's Christian Ruud Ivanisevic dropped to his knees and pounded number one court with his fists in unmistakable delight, coupled with massive relief. He did not stay down for long. "Oh, Jesus, that was a mistake. I was almost burned."

Sampras, facing the 19 year old Slovak Dominik Hrbaty who is playing in his first Grand Slam, found himself 4-2 down in the final set and 15-40 on his own serve. The Sampras tongue was lolling, and the photographers were gathering like king vultures.

It is at times like these, when the American is marinating in his own fatigue that Sampras is a most wonderfully formidable opponent, as he showed in that gut wrenching five set victory over Spain's Alex Corretja in the quarter finals of the US Open last year.

His serve, of course, is his constant strength and succour and again pulled him out of trouble here, although the Slovak, who last year, jumped 287 places in the world, ranking from 364 to 77, had cause rue his own lack of service consistency, his one obvious weakness.

Hrbaty, who has worked his way through satellite and Challenger tournaments, looks richly promising, and perhaps puts Tim Henman's rapid rise to the top 20 in a little clearer perspective.

Like Henman he has a seemingly wonderful temperament and arguably an even greater array of shots. Sampras had never heard of him, let alone played him, and could hardly fail but be impressed it is likely a good deal more will be heard of Hrbaty this year.

Sampras was clearly intent on conserving his energy from the minute he stepped on court, aiming to hit outright winners at every possible opportunity, and not bothering to chase anything that was an obvious lost cause.

This was understandable, for Sampras has no liking for really hot weather, but it did mean the number one seed never really established any rhythm, other than his serve, and in the fourth set Hrbaty patently outplayed the American.

It was a tribute to the young Slovak's rich talent that Sampras had to summon up every ounce of skill and experience to cling on, as he had against Corretja at Flushing Meadow, although this time he admitted to being better prepared, the secret being his consumption of lots and lots of pre match pancakes.

There was much talk of the dangers of playing in such conditions although the heat, for all its severity, was dry. No earth shattering conclusions were reached and the tournament referee, Peter Bellenger, was not unduly perturbed, although he will have the option from today with all the leading matches on centre court of closing the roof.

Ivanisevic also busied himself with conservation of energy against, Ruud. "It's too hot. You cannot try the whole game, otherwise you die," he explained graphically.

At 3-3 in the final set the Croatian was 0-40 down on his serve and in pounded down a whole clutch of aces. "I didn't know where I was. I was just hoping to finish."

The late night match, one of unremitting sweat and attrition, saw Austria's Thomas Muster, the number five seed, survive shoulder, arm, and foot trouble to defeat Jim Courier, winner of the title in 1992 and 93, in four sets.

Courier, trying to club his way back to the top 10, had won their previous seven meetings but these, slowish courts, the more so in this heat, are very much to Muster's liking, not being all that far removed in speed from his beloved red clay.

The match, which followed, Martina Hingis's latest victory, did not finish until well after midnight, and was delayed for more than 30 minutes by a power failure, the suggestion being that with everybody in the city turning up their air conditioning the grid could not cope.

Muster next plays Ivanisevic "Thomas likes to make you run". Sometimes he does not want even to hit winners. He just makes you run, run, run and then you are begging him please hit a winner!" Goran was in splendid form both on and off the court.