By Bianca London and Sadie Whitelocks
Pippa Middleton celebrated her 29th birthday in style last night, by cheering Andy Murray to victory in the US Open quarter-final.
The Duchess of Cambridge's sister donned a vibrant lacy yellow dress, nude wedges and carried a straw handbag at the match.
Once inside the courts she promptly took a seat next to dark-haired, 6ft 3in Spencer Vegosen - a Harvard graduate and accomplished tennis player - before watching the men's quarter final game unfold.
Pippa Middleton and Spencer Vegosen watched Andy Murray play in the men's quarter finals
Avid tennis fan Pippa looked like she was enjoying the game, it was her second day at the tennis
Pippa wore a lacy yellow dress and had her hair in loose curls as she took her seat next to Harvard graduate Spencer
It is not the first time that Pippa has taken a seat next to Mr Vegosen, they both cheered Roger Federer to glory just a day ago on day nine of the competition.
Mr Vegosen, who now resides in New York but is originally from Illinois, Chicago is a familiar face on the sporting scene and he was once one of the top junior tennis players in the U.S, winning 11 sportsmanship awards. His father Jon is also president of the U.S.Tennis Association.
It is believed Mr Vegosen received a BA in East Asian studies and mathematics from Harvard University and spent last summer working in Hong Kong as an analyst for Goldman Sachs. However it is not known where he currently works.
The pair laughed and joked together at the USTA Billie Jean King National Tennis Centre in Flushing, Queens, New York.
Pippa smiled as she watched Murray play and was joined by a brunette friend
Pippa was also joined by a brunette friend and the two seemed in high spirits as they clapped and cheered on the Scottish player who, from the dire straits of 6-3, 5-1 down when he could barely get the ball in the court, fought back to win 3-6, 7-6, 6-2, 6-0 in three hours to keep his Grand Slam dream alive.
After finishing he was able to relax and see who his next opponent would be in his second straight semi-final at Flushing Meadows — whether it would be a rematch of his epic two clashes with Roger Federer at Wimbledon this year or a less expected contest with Czech powerhouse Tomas Berdych.
In the end Berdych shocked Federer in four sets and Murray now has two days to compose himself after making what was an awkward assignment against the 6ft 6in Croat look exactly that.
Avid tennis fan Pippa also attended the match between Tomas Berdych and Roger Federer, as his guest of honour in his box.
Pippa, who turns 29 today, watches the men's singles quarterfinal match between Roger Federer of Switzerland and Tomas Berdych of Czech Republic
Pippa Middleton attended the US open quarter final and took her seat in Roger Federer's private box and cheered on the Swiss player
Roger Federer cut a disconsolate figure as he tried to come to terms with his shock quarter-final exit against an inspired Tomas Berdych at the US Open.
Not since 2003 had Federer lost before the semi-final stage at Flushing Meadows, winning five titles in that time, and he went into the tournament on a high after a stellar summer.
Pippa was spotted after the match bonding with Federer's wife Miroslava Vavrinec Federer as they left the stadium.
Since landing in the metropolis on Saturday to attend meetings about her upcoming book, Celebrate: A Year of Festivities for Families and Friends, Pippa has been snapped with a number of men while sampling some of New York's finer delights.
Pippa wore a bright yellow dress with nude wedges and carried a straw handbag as she left the match
Pippa was seen socialising with Roger Federer's wife Miroslava Vavrinec Federer at the US Open Tennis Center in New York City after the game
In an opulent welcome hotelier Andre Balazs, who is reportedly worth more than $450 million, flew her by seaplane - a trip that costs $525 for a single journey - to his resort, Sunset Beach, on Shelter Island on Sunday.
And later that evening the New York Daily News reported that she was spotted at the Electric Room at Dream Downtown in the Meatpacking district with former New York Ranger Sean Avery.
'She was only there for a short time,' a source told the paper, adding they were there with Mazdack Rassi, owner of photography company Milk Studios.
It has been suggested that Pippa is staying at the Carlyle Hotel located in the Upper East Side, where Roger Federer also has a suite, with two friends, where rooms start at $600 and reach $15,000 - without taxes.
Her trip, during which she is apparently courting the perks of fame, come despite her demands to remain out of the public gaze.
Pippa scored a style ace the day before when she watched Samantha Stosur of Australia play Victoria Azarenka of Belarus during the quarterfinals match
While newspapers have respected her request to be recognised as a private citizen, she still very much seems to be enjoying the high-flying life of a socialite.
Despite her request, U.S. news sites chose to publish photographs of her playing table tennis with Balazs over the weekend, but MailOnline has respected her wishes.
Pippa, who turns 29 today, is in town for meetings over her new book, which is out on October 30. She will not be holding an publicity events for the book while she is here, Viking publishers said.
Billed as a 'comprehensive seasonal guide to simple and creative entertaining', it is a book she hopes will cement her credentials as a party planner, and industry observers believe it could net her a small fortune in the process.
It is believed that Pippa is set to make an appearance at New York's Fashion Week, which kicks off on tonight.