Pennetta beat childhood pal and fellow Italian Roberta Vinci 7-6 (4) 6-2 in the title match in New York, a day after the runner-up engineered one of the biggest shocks in tennis history by ousting Serena Williams.

Speaking of shocks, Pennetta then said in her on-court interview Saturday she was retiring from tennis. At first it was thought Pennetta was stopping now but she later told reporters she'll play until the end of the season.

Pennetta, who will turn 34 in February and almost quit the game because of a wrist injury years ago, became the oldest first-time grand slam champion in the Open Era.

All of Italy rejoiced having two home-grown players in the final -- Italian Prime Minister Matteo Renzi even flew to the Big Apple for the unprecedented occasion -- but pockets of Arthur Ashe stadium, the largest regularly used stadium in tennis with a capacity of about 23,000, were empty.

Had the U.S.'s Williams made the final, it certainly wouldn't have been the case. Chasing a calendar-year grand slam heading into the year's last major, the women's final at the U.S. Open sold out prior to the men's for the first time.

U.S.A. Today reported that after Williams topped older sister Venus in the quarterfinals, the average ticket price soared from around $600 to $1,500. After Vinci stunned Williams on Friday, though, the Associated Press reported tickets could be purchased for $45.

Besides the omission of 21-time grand slam winner Williams, the U.S. Open final featured two players ranked outside the top 20 for the first time since the rankings were introduced. They used to be, however, No. 1 players in doubles.

Fans that did show up for the final, and they were plenty nonetheless -- including actors Robert Redford and Michael Douglas -- saw Pennetta handle the moment better.

She was also able to handle Vinci's backhand slice, the most recognized part of the world No. 43's game. The slice, at times, befuddled Williams and helped to coax 40 unforced errors Friday.

On paper, Pennetta was the favorite. She was better ranked, at 26th, won one of the most prestigious tournaments outside the majors at Indian Wells last year, reached the top 10 in 2009 and held a 5-3 record versus the 32-year-old Vinci. Further, the U.S. Open has by far been her most successful grand slam.

And now she's Italy's second women's grand slam singles champ, following in the quick footsteps of Francesca Schiavone.

Pennetta, a power baseliner with a penetrating backhand, seized the initiative by registering the first break for 3-2, capitalizing on her seventh break chance of the game. Through five games, Vinci didn't hit a winner and committed 10 unforced errors.

Mostly untroubled in her service games, Pennetta blew a 40-15 advantage on serve and suddenly the score was level at 4-4.

Onto a tiebreak they went, and Vinci cracked. From 2-2, she donated four unforced errors, including two on the forehand side. Pennetta sealed the 60-minute opener with a service winner.

The winner of their three previous head-to-head tiebreaks won the match, and Pennetta, who downed grand slam winners or finalists Petra Kvitova, Sam Stosur and Simona Halep to get to the final, ensured a continuation. With all the momentum, she stormed to a 4-0 lead in the second.

Pennetta fended off a fightback by holding for 5-2 thanks to a fine lob, prompting an emphatic fist pump in a match otherwise devoid of much outward emotion. She knew the job was almost done.

It was official a game later. Pennetta broke to love, smacking an inside-out winner on match point, before flinging her racket in the air and exchanging a long hug with Vinci at the net. She later kissed her boyfriend, men's pro, Fabio Fognini.

Waiting for the trophy presentation and in a rare occurrence among players, Pennetta and Vinci sat together. Pennetta called Vinci one of her best friends on tour; they hail from the same region, Puglia, in Italy.

Sunday's men's final sees two familiar names play for the championship. Novak Djokovic, the world No. 1, faces Roger Federer for the second successive time to cap a grand slam.

Djokovic, only the second man in the last 45 years after Federer to make all four grand slam finals in one season, won at Wimbledon and is seeking a 10th grand slam crown.

The evergreen Federer, 34, tries for a men's record extending 18th and first since 2012.

Read: Fognini shocks Nadal