Martina Navratilova and Gabriela Sabatini scored speedy first-round victories today as they began their challenge to top-ranked Steffi Graf in the $2.4 million Australian Open tennis championships.

Three-time Australian champion Navratilova, seeded second, crushed West German Andrea Betzner 6-0, 6-1 while No. 3 Sabatini, playing Down Under for the first time, beat Cecilia Dahlman of Sweden by an identical score.Navratilova's victory took just 50 minutes, while Sabatini was a minute faster.

"I think I am playing really well," said third-ranked Sabatini, who beat Graf twice last year.

"I think I have a good chance to win a Grand Slam event this year."

Navratilova simply overpowered Betzner.

"I'm enjoying tennis more than I have for the past few years," the 32-year-old Navratilova said. "My body isn't hurting any more."

West German teen-ager Graf, winner of all four Grand Slam tournaments last year, began her Australian Open campaign with a victory Monday over Australian Kerry-Anne Guse.

Two seeded American women, seventh-seeded Barbara Potter and ninth-seeded Lori McNeil, fell today.

Powerful New Zealand left-hander Belinda Cordwell beat Potter 6-3, 6-3, while Yuki Koizumi of Japan beat McNeil 6-1, 4-6, 6-4.

Koizumi, ranked 202nd in the world to McNeil's 13th and playing in only the second Grand Slam tournament of her career, coached for 10 years before joining the international circuit last year.