Pippa Middleton attends the 2012 US Open at USTA Billie Jean King National Tennis Center on September 4, 2012 in New York City. Credit: Uri Schanker/WireImage.com

Stealing Kate's style?

Pippa Middleton looked stunning at the 2012 U.S. Open on Tuesday in a blue, orange and green color-blocked dress and Finlay & Co Bosworth shades. The younger sister of Duchess Kate, who is working on a party-planning book, is currently in New York to attend meetings with publishers, a source tells Us Weekly.

Middleton, 28, took a break from her work schedule to watch Victoria Azarenka of Belarus play Samantha Stosuer of Australia in their women's singles match on the ninth day of the U.S. Open. During the match, Middleton was photographed sitting next to Spencer Vegosen. The Daily Mail reports Vegosen is a Harvard grad and tennis player.

According to the credential around her neck, Middleton was a guest of tennis pro Roger Federer. In July, Pippa and her sister Kate cheered on Federer from the stands at Wimbledon in London.

On Labor Day, the famous royal Maid of Honor hit up NYC hotspot Electric Room inside the Dream Downtown and introduced herself to Gossip Girl actor Chace Crawford, 27. "They didn't party together but they spoke for 10 minutes," an insider told Us exclusively. "They had never met before but Chace has met Prince Harry a couple times." The previous day, Middleton spent time with wealthy hotelier Andre Balazs, 55, in Shelter Island, New York. She played ping pong and dined at local restaurant Sunset Beach with Balazs and a handful of friends.