A memorable 2015 women's U.S. Open featuring an unexpected last contest -- an all-Italian showdown in the ultimate match -- went to 33-year-old Flavia Pennetta on Saturday afternoon. The 26th-ranked player in the world knocked off her fellow countrywoman, unranked Roberta Vinci, the player who shocked the world on Friday when she defeated No. 1 Serena Williams in the semifinals.

Pennetta arguably saved the biggest news from the match until after the play was over: her final statement in her on-court post-match interview was that she's retiring from the game.

"Before I start this tournament, one month ago, I take a big decision on my life," Pennetta said. "This is the way I would like to say goodbye to tennis."

The crowd reacted in disbelief.

"I'm really happy," she said. "It's what all players think to want to do, to go out with [and take] this big trophy home. So ... this one was my last match at the U.S. Open and I couldn't think to finish it in a better way."

Pennetta later said she would finish out the season, but has played her last match in a Grand Slam.

Pennetta's send-off for winning her first Grand Slam championship? A $3.3 million payout in her final match. She jokingly handed the check over to Vinci, a longtime friend who was beaming with delight, even in defeat.

"Roberta played unbelievable today," Pennetta said. "She had an unbelievable week. ... We spent so much time together, we could write a book about our life."

Pennetta's unlikely title also included some history: she became the first Italian -- man or woman -- to ever capture a United States Open singles title in tennis.

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

It was a passionate and personal match, as Vinci and Pennetta, who grew up near each other in southern Italy, have known and played against each other for more than two decades. And so the affair in Flushing Meadows, N.Y., on Saturday afternoon was only unfamiliar in that the two had never volleyed and rallied against each other under such heavy stakes before. 

It was in fact the first time either had made a grand slam final, and so this is the first such title for Pennetta, who came out on top with a 7-6 (4), 6-2 victory. Pennetta took the second set with relative ease after both players broke the other's serve in the first set. The match, which took place under darkening skies and with a sprinkling of rain, took one hour and 33 minutes to complete. 

For some perspective on just how unlikely this title match was: Pennetta went 17-15 in 2015 prior to her seven straight match victories en route to this U.S. Open, while Vinci's only match win in 2015 majors prior to the U.S. Open came in the first round of the Australian Open. Pennetta was 150-to-1 to win the title prior to the U.S. Open.

In terms of major-championship play, Pennetta and Vinci had previously met in a major, the U.S. Open in fact, when Pennetta won 6-4, 6-1 in 2013.

Vinci, who stands 5-foot-4 and is ranked 43rd in the world, is second shortest woman ranked in the top 50. Her signature backhand spin and drop-shot game wasn't enough to match Pennetta's baseline and powerful two-handed backhand attack.

"It was tough the past 24 hours with a lot of things on my mind," Vinci said. "I was a little bit tired ... but, you know, I lost in the final. I'm really happy, I'm really happy for Flavia."

Pennetta broke Vinci in the fifth game of the first set to take a 3-2 advantage. Vinci broke back in the eighth game to tie it at 4-4, then went up 5-4. But Pennetta's strength, foot movement and agilitly along the lines helped her come back to win the tiebreaker 7-4.

That was essentially the match, as Vinci was inconsistent and unable to keep Pennetta on her heels for most of the second set.

The longtime friends met at the net after the match, both flashing huge smiles and embracing in a big hug. This was a huge day for Italian tennis, maybe the biggest one ever.

And while Pennetta is stepping away from the game, the affable Vinci doesn't seem to be slowing up just yet. After receiving her runner-up trophy, Vinci said to the New York crowd shed clearly won over, "See you next year, guys. Come to watch."

Flavia Pennetta (USATSI)
Flavia Pennetta beats Roberta Vinci to win the US Open on Saturday. (USATSI)