Serena Williams vs Venus Williams in US Open Tonight

According to NJ.com, as Serena Williams goes for the Grand Slam, there remains one formidable obstacle in her path to the U.S. Open championship and the final leg of her historic quest:  It's her sister, Venus.  On Tuesday night in prime time, the No. 1-seeded Serena faces 23rd-seeded Venus at Arthur Ashe Stadium in the women's quarterfinals at Flushing Meadow, N.Y. Will Serena's sister be the one to deny her an even bigger place in tennis history?  

"I don't think anyone wants to be a spoiler. I think people love to see history being made," Venus said. "No one is out to be a spoiler, but at the same time, you're focused on winning your match, even though the circumstances are really much different."

"Even though you're playing your sister, you have to be prepared and focus. The preparation doesn't change."  It's a familiar role for Venus, who is 15 months older. She was the opponent in every final when Serena won four major titles in a row from the 2002 French Open to 2003 Australian Open. Serena holds a 15-11 edge overall as pros.

And, of course, the two have been playing against each other since they were children.

"I used to always win," Venus said, "in the early days."

Here's what you need to know:

What: U.S. Open women's quarterfinals

Time: 7 p.m.

TV: ESPN