ANDRE AGASSI triumphed in a battle of wills to beat Jim Courier in five sets and reclaim the number one position in the world rankings. Only Michael Chang stands between Agassi and another, Australian Open final appearance as his title defence, stepped up a few notches in a rousing, 6-7 (7/9), 2-6, 6-3, 6- 4, 6-2 victory in a match carried over from Tuesday because of rain.

It was Agassi's third five set battle at this year's Open, but yesterday's win had added significance - Agassi stopped a six match losing sequence against his long time rival Courier and denied Austrian Thomas Muster the chance of leapfrogging him to claim the top ranking from Pete Sampras.

Agassi meets fifth seeded compatriot Chang in tomorrow's semi final.

Boris Becker also sounded an ominous warning to his rivals after defeating confident young Russian Yevgeny Kafelnikov in their quarter final.

Becker, who revived his ailing form last year appearing in the Wimbledon final and winning the Grand Slam Cup, destroyed sixth seeded Kafelnikov, 6-4, 7-6 (11/9), 6-1 in one hour, 52 minutes.

Becker will face unseeded Australian Mark Woodforde in tomorrow's semi final.

Woodforde, ranked 67th in the world, upset seventh seeded Swede Thomas Enqvist, 6-4, 6-4, 6-4 in two hours five minutes in last night's final match to reach his first Grand Slam semi-final. Woodforde (30), playing in his 38th Slam event, is Australia's first Grand Slam semi-finalist since Pat Cash in Melbourne in 1988.

Earlier, Becker rated his straight sets demolition of 21 year old Kafelnikov among his tap three wins in Australia in 10 visits to the event. "I said after I won my first two matches here (both five setters) after struggling hard and being down twice that maybe that was a good sign for me, I worked my way in and I had plenty of practice on the match courts," Becker said.

Becker's windmill serve was his main weapon against Kafelnikov. The German slammed down 28 aces against the Russian, who had not been beaten in nine matches, in Australia this summer. "He had been playing extremely well in the last three weeks, he hadn't lost a match, and I knew that I had to be really alert at the beginning and to play with my strengths and try to mix up my game," he said.

"I think he was offguard with my strokes from the backcourt, he didn't think I could play that well from the back, plus my serve was on so he was under constant pressure for the whole match."

The triple Wimbledon champion, who had won two of his previous three encounters with Kafelnikov, all indoors, fought back from 1-5 down to take the second set tie breaker 11-9 and swing the quarter final his way.

Kafelnikov, who spoke earlier this week of his confidence in winning the Australian major title, praised Becker's performance. "I knew it was going to be a difficult match. That's what makes the difference between the greatest players and a good player, there's no question Boris is a great player."

Woodforde, who finished the match with Enqvist flat on his back at the realisation of his achievement, said it was a sweet feeling. "It's quite incredible, words can't describe it and it's so exceptional that this is all in my own backyard."

Germany's Anke Huber ended the Spanish women's challenge by knocking out second seed Conchita Martinez in three sets to go into only her second Grand Slam semi final.

Huber, the 21-year-old world number nine, came back from a set down to beat Martinez 4-6 6-2 6-1 in an hour and 44 minutes in a match disrupted by rain.

Martinez, a semi-finalist in the last four Grand Slam events, bows out with compatriot and third seed Arantxa Sanchez Vicario, who was beaten in Tuesday's marathon match, against US teenager Chanda Rubin.

In an error riddled match, Martinez had held her game together more than a wayward Huber in the first set but then fell behind 3-1 in the second when the heavens opened on the Flinders Park Centre Court and play was stopped.

When the match restarted about 45 minutes later under lights and with the sliding roof in place, Martinez slipped heavily with the score at 4-2, grazing the knuckles on her right hand and slightly injuring an ankle.

She went on to lose the set 6-2, and fell behind 3-0 in the decider, losing 11 straight points with a succession of drives landing well over the baseline.

The injury was treated but Huber, scenting victory, took the ball earlier and with her forehand at last finding its range and direction, kept up the momentum to break for a third time to take the match at 6-1.

Martinez's defeat means that Spain will be unrepresented in the women's singles semi finals for the first time since 1990. Rubin, the conqueror of Sanchez Vicario, plays top seed Monica Seles while eighth seeded Huber meets South African Amanda Coetzer, who ended Swiss teenage prodigy Martina Hingis's hopes of becoming the youngest ever Open semi finalist.

Coetzer taught the 15-year-old a lesson in accuracy, using unerring ground strokes and a determination to run down every ball to win 7-5 4-6 6-1 in difficult, blustery conditions.

An anguished Hingis, playful in victory in her historic quarter final win against 11th seed Brenda Schultz McCarthy, threw or grounded her racquet 11 times' as she made dozens of unforced errors.