NEW YORK -- Once upon a time, Venus Williams whipped all comers. Little sis included. So big was her serve, so forceful her strokes, it seemed she might rule the sport forever.
Reminded that those halcyon days took place nearly five years ago, Serena Williams was taken aback.
"Has it been that long?" she asked.
It has. And almost as long since Serena supplanted her older sister as the premier player in women's tennis.
Come Sunday, everything old will be new again. In a match that marks their subsequent slides -- and is sure to measure the extent of their respective returns -- the Williams sisters will square off in fourth round of the U.S. Open.
Venus defeated Slovakia's Daniela Hantuchova 6-3, 6-3 and Serena stopped Italy's Francesca Schiavone 6-3, 6-4 at Arthur Ashe Stadium on Friday, setting up a round of 16 showdown between a pair of siblings whose last two Open meetings came in the 2001 and 2002 tournament finals.
"Every single point will be [important]," Venus said. "More than anything I'll just have to compete better. I got a lot of tricks from Serena just watching her. She inspired me so many times. I got motivated by her in the early part of my career, and even now."
Though the circumstances have changed -- the previous finals were glitzy, star-studded affairs -- the sisters' distaste for playing each other remains constant.
The Williamses last met in Miami this spring, with Venus topping Serena in straight sets, 6-1, 7-6(8) to snap a six-match losing streak against her younger sister.
"It's obviously extremely disappointing to have to play my sister in the next round," Serena said. "But I can't tell you the disappointment. Hopefully one of us will be in the quarters and we'll just have to go from there."
For a duo that owns 12 major titles between them -- and has met in six Grand Slam finals -- a fourth-round match is both a comedown and a benchmark, as well as the sisters' earliest meeting in a major since the 1998 Australian Open.
Their still-glimmering celebrity aside, Venus and Serena are hardly in vintage form: each has struggled with injuries and distractions, not to mention a women's field that has raised its collective level of play.
The sisters' skids commenced after Serena's victory in the 2003 Wimbledon final, a match that saw Venus re-aggravate an abdominal strain. Shortly thereafter, Serena underwent left knee surgery.
Both missed that year's Open. Neither won a major title last season. Their father, Richard, publicly speculated that Venus might retire and that Serena was distracted by outside interests.
Frankly, the point was hard to argue. Serena slipped from No. 3 to No. 7 in the year-end rankings. Venus languished at No. 9. After nearly a decade on the WTA Tour, the two former No. 1's seemed preoccupied: Venus by her interior design business, Serena by the fruits of full-blown divahood -- acting gigs, fashion design, dating porcine Hollywood director Brett Ratner.
"I'm definitely no Mariah Carey, I'm definitely no Madonna," Serena protested on Friday. "That's for sure. To even be put in that category is definitely kind of cool."
This season, however, has brought a partial revival. Serena won the Australian Open; Venus outlasted Lindsay Davenport in a dramatic Wimbledon final. Since the latter, each has missed time -- Serena with a sore ankle and knee, Venus with the flu and exhaustion.
As such, the sisters are still rounding into form, with Venus appearing slightly sharper than Serena.
Earlier this week, Serena said she would have to perform at "80 or 90" percent to compete with her older sister.
"She's playing unbelievable," Serena said. "I'm just going to have to pick it up. Each game I'm picking up the level of my play."
No. 10 seed Venus had little trouble picking up her play against Hantuchova, breaking the No. 20 seed four times. As for No. 7 seed Serena, she had less trouble with No. 25 seed Schiavone than her 10-karat diamond choker, which came undone near the end of the match.
Serena also was sporting her now-famous $40,000 chandelier earrings, a loaner piece she said would be auctioned after the Open to benefit victims of Hurricane Katrina. She previously promised to donate $100 for every ace she hits the rest of this season.
After her second-round match, Venus responded to a Katrina question by saying she didn't watch the news
-- a statement that prompted a subsequent article accusing the sisters of feeding "every bad stereotype about rich, spoiled, self-absorbed athletes."
On Friday, Serena responded to the criticism.
"How was that?" she asked. "I think I actually made a very kind gesture out of nowhere I don't live the elaborate life. The diamonds are borrowed. I won't buy them because I'm too cheap I don't understand where [criticism] is coming from."
For her part, Venus said her comments were taken out of context and announced the sale of $1 yellow shoelaces -- a la Lance Armstrong's LiveStrong wristbands -- with the proceeds going to Katrina relief.
"Everyone's trying to do something," she said. "This is a sad time. Everyone's in my prayers."
The sisters were decidedly less somber -- or even serious -- when discussing their impending match, the 15th of their professional careers. Asked how she prepares for Venus, Serena simply smiled.
"When I was winning all the Grand Slams, I poisoned her food," she said. "I may have to go back and do that again. I put this little special thing in there to make her not move her feet, not run to the ball."
Told of her sister's scheme, Venus had a quick rejoinder.
"She doesn't know that I have a food taster," she said.
Patrick Hruby is a Page 2 columnist for ESPN.com.