NEW YORK – As the U.S. Open begins Monday, the women’s title is considered up for grabs, with perhaps half a dozen serious title contenders. And yet this Grand Slam, just like women’s tennis as a whole, is in many ways all about the Williams sisters.

Only one active player owns more major singles titles than Venus Williams’ six: Serena Williams, with eight.

Each Williams took home one of this year’s first three Grand Slam trophies: Serena at the Australian Open, Venus at Wimbledon.

They are the primary reason the U.S. Open’s women’s championship shifted to prime time in 2001, when they met in the first of six all-Williams major finals.

And they are featured in the two matches under the lights Monday night at Arthur Ashe Stadium on Day 1 of this year’s U.S. Open. Top-seeded Justine Henin, No. 3 Jelena Jankovic and No. 5 Ana Ivanovic are in action during the day, as is three-time defending men’s champion Roger Federer.

It’s quite clear: Regardless of what the rankings or recent form say, any conversation about women’s tennis, where it’s been and where it is, begins with the two big-hitting siblings.

“Growing up, we dreamed of that, of us being on top of women’s tennis, playing Slam finals, being (ranked) 1 and 2. That’s what we worked for,” said Venus, who faces 137th-ranked qualifier Kira Nagy of Hungary. “So when that happens, it’s incredible, it’s amazing. I think for us there’s no doubt that we can achieve these things.”

And still, in so many ways, the Williams sisters are about so much more than women’s tennis, from their clothing deals to various outside interests.

“Their passions get inflamed for tennis at times,” said CBS analyst Mary Carillo, “and at times it seems the only place they want to be is away from the sport.”

That’s particularly so when it comes to Serena, the younger, more everywhere-you-turn-there-she-is of the pair.

She has a provocative photo in the August issue of Jane magazine, her back to the camera, wearing nothing but a silver pair of heels and holding a strategically placed bunch of flowers. “I’ll take off my shirt in a second – locker room girls don’t have much shame,” the accompanying copy reads.

Her take on the picture? “Simply divine,” she said Saturday.

And as of Tuesday, she’ll loom over midtown Manhattan on a billboard for a Nike ad campaign featuring female athletes. The tag line: “Are you looking at my titles?”

Let’s not forget, too: This is someone who was asked after losing a Wimbledon final what advice “as a tennis superstar” she would offer the new champion and replied, with a laugh: “I’m not a tennis superstar – I’m a superstar. I’m just kidding. I don’t want to sound like I’m pontificating or anything. Although, I am a little bit.”