US Open 2015: Flavia Pennetta beats fellow Italian Roberta Vinci to title - and then announces her retirement from tennis

150/1 outsider becomes oldest female in the Open era to win a first Grand Slam

Flavia Pennetta celebrates after defeating her compatriot Roberta Vinci in the final of the women's singles at the U.S. Open (Reuters)

Italy's Flavia Pennetta became a shock grand slam champion by winning the US Open title and then revealed another surprise by announcing her retirement from tennis.

Pennetta was rated 150/1 to triumph at Flushing Meadows before the tournament began but became the oldest female in the Open era to win a first Grand Slam after overcoming fellow Italian Roberta Vinci 7-6 (7/4) 6-2.

Vinci's challenge was even more of a surprise, having knocked out top seed Serena Williams in the last four on Friday, but the world number 43 failed to repeat her heroics in what was the Open era's first all-Italian major final.

Pennetta, aged 33, flung her racket into the air after sealing victory in one hour and 33 minutes, before embracing her compatriot with an affectionate hug at the net.

The champion addressed a jubilant crowd in Arthur Ashe Stadium but as the interview concluded, she asked to take the microphone for one more announcement.

"I am going to retire from tennis," world number 26 Pennetta said.

"This is what all players want to do, go out taking a big trophy home.

"This is my last match at the US Open and I couldn't finish in a better way."

It was a suitably unpredictable finish to a baffling tournament that had just witnessed a final contested between two players with a combined ranking of 69, age of 65, and who had never before made a grand slam final between them.

It is only the seventh time a female player from outside the top 25 has won a major title and Pennetta's success in her 49th grand slam is the longest a woman has ever had to wait to achieve the feat.

"I am really happy, I have to say before this tournament I never think to be so far, I never think to be champion," Pennetta said.

"That's why it's amazing, this is coming as a big surprise for me. It's a dream come true."

Only two weeks ago, Pennetta and Vinci, girls doubles winners together at the 1999 French Open, were having dinner in New York, oblivious to the extraordinary tournament about to unfold and which will surely define both their careers.

Vinci admitted her shock win over Williams, which ended the American's hopes of a first calendar grand slam since 1988, had been the greatest day of her life and perhaps it was too much to expect the 32-year-old to recover her poise less than 24 hours later.

Pennetta's run to the final was less mind-boggling - she reached the semi-finals here in 2013 - but no less impressive, given she had to beat Samantha Stosur, Petra Kvitova and Simona Halep along the way.

Both players started nervously, chipping shots safely down the middle of the court but Pennetta was the more consistent and after a lengthy game, she converted her seventh break point to lead 3-2.

Vinci had unsettled Williams with her change of pace, variety and wily slice backhand, which she relied on again to great effect, breaking back for 4-4 when a Pennetta backhand hit the net.

Neither player were forceful enough to make another breakthrough and the set drifted into a tie-break, where Pennetta made her extra quality from the baseline count.

A loose Vinci forehand long gifted away the first mini-break and Pennetta capitalised, serving out with ease to clinch the opening frame.

Vinci took a toilet break but could not halt the momentum in the second set, as her opponent, now hitting more freely, cruised into a 4-0 lead.

A break back and hold reduced the deficit and gave Vinci temporary hope, but Pennetta was not about to let this opportunity slip as a forehand winner confirmed victory and sealed her most unpredictable of triumphs.

PA