Former world number one Steffi Graf continued her comeback from an injury-plagued 1998 yesterday, beating American Serena Williams to reach the quarter-finals of the $750,000 Adidas International in Sydney.

The 29-year-old Graf played only a handful of tournaments in 1998 because of a series of injuries after being out for most of 1997 due to injury as well.

But she came back with a fury late last year and began this year ranked number nine in the world after winning two of the last three tournaments she entered and 12 of her last 13 matches.

She continued that roll against Williams, beating the American teenager 6-2, 3-6, 7-5 in almost two-and-a-half hours to reach the quarter-finals of the Australian Open warm-up where she will face Venus Williams, the elder of the two sisters.

Graf broke the 17-year-old Williams's first two service games to take a 4-0 lead.

Williams, who reached the semi-finals of last year's tournament by beating current world number one Lindsay Davenport before losing to eventual winner Arantxa Sanchez-Vicario in the semis, came back to win the second set 6-3.

The two traded breaks to open the third set before Graf exerted her authority to close out the closely fought final set 7-5, breaking Williams to win the match.

Venus Williams, who is world number five, could be Graf's toughest match in the lead-up to next week's first Grand Slam of the year.

She overpowered South Africa's Amanda Coetzer 7-6 (7/5) 6-2 to win the right to face the German.

Defending champion Arantxa Sanchez-Vicario of Spain, who had a bye in the first round, beat Germany's Anke Huber 2-6 6-3 62 to win a berth in the quarterfinals where she will face Austrian Barbara Schett.

Davenport beat fellow American Mary Joe Fernandez 6-4 7-6 (8/6) to get into the quarter-final round where she will face Switzerland's Patty Schnyder who overran Slovakia's Karina Habsudova 6-4, 4-6, 6-4.

Martina Hingis will play Dominique Van Roost of Belgium who easily dispatched Russian glamour girl Anna Kournikova 6-1 6-2.

Men's top seed and world number three Alex Corretja overcame Switzerland's Marc Rosset 4-6, 63, 7-6 (7/2) while fellow Spaniard Albert Costa beat American JanMichael Gambill 6-3 7-5.

Brazil's former French Open champion Gustavo Kuerten beat

Australia's Todd Woodbridge 6-4, 6-0 and will meet defending champion and fourth seed Karol Kucera of Slovakia.

Kucera out-served Cedric Pioline of France 6-4, 6-0 in 61 minutes.

Australian teenager Lleyton Hewitt, who ousted world number four Pat Rafter in the first round, continued his run-up to the Australian Open, defeating German Nicolas Kiefer 6-4, 6-2.

And Jason Stoltenberg of Australia beat former Wimbledon champion Richard Krajicek of the Netherlands, seeded sixth, 6-3, 6-4

Lindsay Davenport and Steffi Graf called yesterday for a new probe into why the International Tennis Federation (ITF) let Czech star Petr Korda off for a drugs offence.

Davenport and Graf questioned Korda's claim that he did not know how the detected steroid had got into his system when he tested positive for a banned substance at Wimbledon.

"It seems to me that they've now set a precedent. . . if I ever get caught I'm just going to say `I don't know how it got there' and every other player is going to say that," Davenport said.

Graf also questioned why the ITF did not suspend Korda for one year from Grand Slam events.