The once invincible Venus Williams is now thoroughly ordinary, but her sister Serena still has a hex over Amelie Mauresmo.

Serena clobbered the disappointing Frenchwoman, 6-2, 6-2, under a 90-degree sun Tuesday afternoon in the Australian Open quarterfinals. It was Serena’s ninth win in 10 matches against Mauresmo, and gave her another crack at Wimbledon champion Maria Sharapova, who defeated Svetlana Kuznetsova 4-6, 6-2, 6-2.

Mauresmo, seeded second, wilted once again in the second week of a Grand Slam, this time with her injured hamstring wrapped tightly. She was lucky to win as many games as she did against Serena.

As for Venus, it’s not just that she lost her fourth-round Australian Open match Monday evening to Melbourne’s darling, Alicia Molik, but how she did it. For nearly two hours, Molik put Venus on the defensive and eventually overpowered her, an achievement that would have been unthinkable four years ago.

Molik, a late bloomer at age 23, earned a 7-5, 7-6(3) victory that catapulted her into the top 10, the first time an Australian woman has reached such heights in 20 years. In a sport heavily populated with teenage girls, the ever aggressive Molik plays more like her countryman Mark Philippoussis: Crank the serve, rip the forehand and move forward when she can. Her second serve, which kicks up high to her opponent’s backhand, is considered the best in women’s tennis.

Molik stands 6 feet tall and weighs 160 pounds, and only recently has she come to terms with her physical gifts. In the past year, she’s worked hard to improve her fitness, and she now plays with more purpose and thought. She’s won 12 consecutive matches this season, including a title in Sydney the week before the Australian Open. This was her first victory in four tries against Venus and the first time an Australian woman has reached this tournament’s quarterfinals since Anne Minter did it in 1988.

Afterwards, Venus was not in a sporting mood.

“It was definitely a match I should have won,” she said. “Normally if I’m playing 5% better, this match is going to be mine.”

Molik is hardly one to gloat, but her assessment of the match was more on target: “I beat her playing my tennis,” she said. “I didn’t wait for her to make mistakes.”

Molik next faces top seed Lindsay Davenport, whom she has never beaten. The winner of their match will be favored to reach the final after taking on either Nathalie Dechy or Patty Schnyder.

Molik played most of her forehands to Venus’s backhand and varied the pace and placement of her serves, even firing a second-serve ace. Though movement is not one of her strengths, Molik hustled and flicked a backhand lob winner off a drop volley from Venus, giving her a 5-4 lead in the second set. Venus, in contrast, moves exceptionally well, but she continues to struggle with her technique and balance once she arrives at the ball. It’s as if she now has three or four different forehand swings, a sure recipe for unforced errors.

Molik started the match with an ace and took advantage of some casual Venus errors to earn an early break and a 3-1 lead. Venus immediately broke back, and the two held serve until Molik led 6-5. Playing loose points once again, Venus fell behind love-40 and dropped the set when Molik forced her into an error with a forehand blast.

Molik’s best moments came in the second set. At three games all, she fell behind 15-40 but stuck to her guns. She nailed a first serve and followed it up with a penetrating forehand. After gaining the advantage, she sealed the game with the fourth of her seven aces.

In the tiebreak, Molik took it to Venus, firing an ace and stepping around her backhand to rip a forehand winner. Down 5-1,Venus could only recover two more points before she awkwardly patted a forehand into the net. The hometown fans roared as Molik jumped and pumped her fists.

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HEWITT DEFEATS NADAL IN MARATHON MATCH In Monday’s afternoon session, Australia’s other great hope, Lleyton Hewitt, survived a grueling five-set battle with young Spaniard Raphael Nadal, 7-5, 3-6, 1-6, 7-6(3), 6-2.

Up to this point, Hewitt’s only problem has been his mouth, which annoyed his two previous opponents, James Blake and Juan Ignacio Chela. After one trademark “Come on!” from Hewitt, Chela tried to hit the Australian with a serve and later spat in his direction, resulting in a $2,000 fine.

For most of his match against Nadal, Hewitt had little to celebrate. He fell behind early in the first set before coming back to win it, and then Nadal took over. The 18-year-old is a much-improved player from a year ago, when he lost to Hewitt in straight sets here. Few strokes in the men’s game look as wonderful as his long, fluid, left-handed forehand, which creates impossible angles with tight, looping spin. He has an affinity for the spotlight, too, as he proved in several key victories during Spain’s charge toward last year’s Davis Cup title.

Hewitt, who has played incredibly consistent tennis since last summer, made numerous uncharacteristic errors. He sustained a hip injury before this tournament began, and he said it flared up throughout the match. By the end of the third set, he looked defeated.

Then, suddenly, Hewitt perked up. Fighting to stay in the match, Hewitt climbed back from 15-30 to take a 6-5 lead. In the tiebreak, tension mounted, with both players hitting difficult winners and also giving away easy points with bad errors. Hewitt, the king of gritty tennis, kept knocking the ball over the net, closing out the set when Nadal slapped a forehand wide.

Nadal’s serve is his biggest weakness, and he could not recover from a love-40 hole in the first game of the fifth set. Hewitt broke serve on Nadal’s third backhand error of the game, and then he began to gather steam. Within minutes he was ahead 3-0, and Nadal was finished.

Though he walked away victorious, Hewitt’s prospects of making the finals have dimmed considerably. First up, he’ll have to get past another hot day and David Nalbandian, a patient and steady player who will make Hewitt work hard for a win. And if Hewitt does reach the semifinals, Andy Roddick will almost certainly be there, well-rested and serving rockets.