MELBOURNE, AUSTRALIA, JAN. 19 (TUESDAY) -- Top-seeded Ivan Lendl powered his way into the semifinals of the Australian Open Tennis Championships today, beating the last surviving American in the men's singles, Todd Witsken.

Lendl will face either Wimbledon champion Pat Cash of Australia or Michiel Schapers of The Netherlands, who played later. Cash, seeded fourth in the year's first Grand Slam tournament, defeated Lendl in the 1987 Wimbledon final.

In the women's draw today, three-time champion and second-seeded Martina Navratilova had to struggle to beat No. 6 Helena Sukova, 6-4, 7-6 to reach the semifinal round. It took Navratilova, 31, 75 minutes to win and continue her quest to reach a 12th straight Grand Slam final.

It was Sukova who ended Navratilova's record 74-match winning streak in the 1984 Australian semifinals. As this match progressed, it appeared another such upset could be brewing.

In the first set she was unable to combine accuracy with her power and unable to dominate at the net. But she volleyed more impressively in the second set and Navratilova briefly appeared rattled before taking the tie break by winning the last six points.

Navratilova, who has won the last two Grand Slam tournaments, Wimbledon and the U.S. Open, captured the Australian Open singles title in 1981, 1983 and 1985. She now has a 19-2 career record against Sukova.

"I just hope history doesn't repeat itself," said Lendl, who lost to Cash in the semifinals of last year's Australian Open.

The reigning U.S. Open and French Open champion, Lendl, 27, took 2 hours 13 minutes to eliminate Witsken, 6-2, 6-1, 7-6. The 24-year-old former University of Southern California all-America from Carmel, Ind., had upset seventh-seeded Henri Leconte of France on his way to the quarterfinals.

But Witsken, who upset Jimmy Connors in the 1986 U.S. Open, simply had no answer to Lendl's pressure.

Lendl, seeking his seventh Grand Slam title, but his first Australian Open crown, and the 71st tournament victory of his career, has yet to drop a set in the tournament.

Witsken made a number of errors, but Lendl wore down his confidence with his power and consistency from the base line.

The American was able to solve Lendl a little in the third set, rallying from 1-3 to force a tie break.

The two remaining men's quarterfinals are scheduled for Wednesday.

Stefan Edberg of Sweden, looking for his third straight Australian Open singles title, faces unseeded Andrei Chesnokov of the Soviet Union and two-time champion Mats Wilander will play fellow Swede Anders Jarryd.