Pippa Middleton is again courting attention after her US Open appearance as the guest of the tennis world's top man.

Number one seed Roger Federer invited the future King of England's sister-in-law to Flushing Meadows for day nine of the open. And she dressed to kill.

A tennis fan herself, Middleton - sister of Prince William's wife, Kate - wore a ''figure-flattering'' colour block dress and accessorised with tan wedges, a straw Kate Spade handbag and a personal guest pass as she posed  for photographers outside the venue, the Daily Mail reported.

Ahead of the women's singles quarterfinals, Middleton took her seat next to the suave, 6ft 3in (that's 190cm), Harvard graduate - and fellow tennis player - Spencer Vegosen, 24.

Vegosen, the Mail reported, was one of the top junior tennis players in the US and his father, Jon, is president of the US  Tennis Association.

Vegosen studied East Asian Studies and Mathematics, and is said to know Mandarin Chinese, Classical Chinese, Japanese and Spanish. He was also believed to have worked at Goldman Sachs, The Telegraph reported.

Reports suggest Middleton is staying with two friends at the Carlyle Hotel in New York’s Upper East Side. It is the same hotel where Federer also has a suite. The price tag for rooms start at US$600 and reach US$15,000 without taxes.

The Mail added Middleton turns 29 on Thursday (local time) and was in the city for meetings over her new book, due out on October 30.

And in spite of her requests to be kept out of the spotlight, Middleton is understood to be making an appearance at New York’s Fashion Week when it kicks off this week.

The pair watched the women's singles quarter final match between Samantha Stosur of Australia and Victoria Azarenka of Belarus. Azareka prevailed 6-1 4-6 7-6 (7-5) in a thrilling contest lasting almost two-and-a-half hours.

- © Fairfax NZ News