Remember back in 2001 and 2002, when these two fun-loving, loss-hating sisters met in the final? Then, the match-up wasn't quite the pick 'em that it is now, as Venus was clearly the better player coming off her '01 Wimbledon triumph, and Serena was a head above Venus the next year, having already taken down her older sister in the 2002 Roland Garros and Wimbledon finals.

Things aren't quite as clear this time around. Venus is coming off her fifth Wimbledon title but hasn't won a significant outdoor hard-court title in six (gulp) years. Serena had a fairly impressive four months of the year but finds herself Slam-less and without a title since Miami.

Moreover, they have both looked very good in their four matches -- borderline great. Serena has only dropped 14 games, while Venus has only let go of 15.

“At least so far I'm winning in something,” said Serena, who is still smarting to her loss to Venus in the Wimbledon final.

A quarterfinal might be too early for the sisters to meet based on form, but perhaps more than anything else, the ranking system supports the cliché, “It is what it is.” If the sisters were ranked Nos. 1 and 2, they wouldn't have this problem.

But they are and have had more than their fair share of struggles since the summer of 2003, when both sustained serious injuries and, consequently, their rankings and level dropped. Serena has won two Aussie Open crowns since then, and Venus has picked up three Wimbledon crowns, but they have never even come close to dominating the tour like they did between 1999 and the first half of 2003.

Now, the 28-year-old Venus says they are back in near-peak form, although 26-year-old Serena, who is more the perfectionist and is much harder on herself, begs to differ with how well she's playing.

“I know that I can do better because I know my game. I feel like I've played better. I'm serving well and making a lot less errors, which is definitely something that I wanted to do,” said Serena. “I just know I can get there. I feel like I can win the tournament if I play my best tennis. I don't think I've played my best yet. I feel like I can play better.”

Serena owns eight Grand Slam titles, while Venus has seven. They are 8-8 against each other lifetime and, remarkably, 5-5 against each other at the Grand Slams. In the four-year period from 1999-2002, the sisters reigned supreme at the US Open, with Serena winning her first Slam title in 1999, Venus snaring the next two crowns in 2000 and 2001, and Serena again raising the trophy in 2002. Neither has been back to the winner's circle since then, but they have faced off in Ashe Stadium on another occasion -- when Venus stopped Serena in the fourth round in 2005.

“I would love to win this championship,” said Venus. “I have to meet her in the quarterfinals, and that will be a huge milestone to get by her to win this championship.”

Venus failed to do that in 2005, when eventual champion Kim Clijsters stopped her. But she appears to be more healthy now, having taken off a significant amount of time between Wimbledon and the Olympics. She's rushing the net like a demon, serving hard and with a very high percentage, and controlling action off the ground.

“Nowadays, I throw in a slice and loopers,” she said. “I don't know what's gotten into me. I guess it just comes, and that's good, too. So I like coming in. If I can have the opportunity to move forward, that's how championships are won. I know that, and I've done that before, so I'm definitely going to keep doing it.”

Despite her own misgivings about her level, Serena has been putting on clean, authoritative performances. There is almost nothing to quibble about with her game: her cross-court forays have been sharp and deep, her vaunted returns down the line have hit their spots, she's owning all of her wide-variety serves, and she's making some keen mid-match adjustments.

On Monday night, she already had her game face on. She was deadly serious in press, never cracking a smile. She hasn't met her major goals this year, meaning at least one of the first three Slams or the Olympics, and she'a burning with desire to take a major in 2008.

“I hate to lose,” she said. “It doesn't matter who I'm playing. This is only the quarterfinals, and I really just kind of want to do well, whether I was playing anyone else on the tour. So I'm just trying to be really serious about it.”

Given that it's the 17th clash of their career, both women are past the point where it will be a lovey-dovey affair between two very close siblings.

“It's my career and her career,” Serena said. “I know she can definitely bury it. I have to do the same thing: just do what it takes to win.”

Very little separates on court: Serena has a slightly better forehand; Venus a slightly better backhand. Venus' first serve has more pop, while Serena's second serve is less attackable. Both can scald returns and can run like the wind. Venus has been more willing to come to net, but Serena can volley more than a touch, too. Both are now smart veterans who know when to change it up when necessary.

The winner of this match will be the one who executes better, plain and simple. That player will be Serena, who will win a few more of their extended rallies and make mincemeat of Venus' second serves. Take Serena in three mentally weighty sets. And have fun watching it.