By Julian Linden
With Serena missing through injury this year, Venus has opted out of the doubles to focus on singles and her form so far has been illuminating, advancing to the last four without dropping a single set.
"I've always played pretty well here," said Venus. "I feel really comfortable here, and it's great to come back to a place where I have won and a place where I've played well. So all in all, I feel positive."
The Belgian completed a fairytale return to New York when she won last season, celebrating her victory on court with her infant daughter, and says her unexpected success last year has provided her with the confidence she can do it again.
The pair have played each other 12 times since 2001, winning six times each. Williams was the dominant player in their earlier clashes but Clijsters has won the last four, including a classic three-setter at last year's U.S. Open quarter-finals.
Wozniacki, promoted to the top seed this year because of the absence of world number one Serena, made the final against Clijsters in 2009 but is a more confident player now.
The 20-year-old won three lead-up events last month to finish as the leading pointscorer in the U.S. hardcourt series. If she wins the U.S. Open she will collect a bonus cash prize of $1 million and replace Serena atop the world rankings.
The Dane has sailed through her matches without dropping a set and developed a killer's instinct to finish off her opponents quickly.
"I'm really competitive," she said. "I really don't like losing."
The pair have played each other just four times before, all in the last two seasons, splitting them two apiece.
Zvonareva, six years older than Wozniacki, has taken longer to hit her straps and will be appearing in her first U.S. Open semi-final, but the seventh-seeded Russian is now flush with confidence after reaching the Wimbledon final in July.
"What does it say? I guess I'm improving. I'm still improving, you know," said Zvonareva. "I've been playing for a while, but I'm still out there and still working hard. I'm still improving."
(Editing by Frank Pingue)