Most fans in the United States expected to watch Serena Williams in the 2015 US Open women's final but that will not be the case on Saturday, as two Italians are set to face off for the coveted Grand Slam.

Roberta Vinci and Flavia Pennetta will collide for the 2015 US Open women's title on Saturday at Arthur Ashe Stadium, just a day after scoring upset victories against their respective foes on Friday.

Pennetta, the 26th seed in the women's draw, booked the first final seat after scoring an easy 6-1, 6-3 victory over second seed Simona Halep of Romania in the semifinals.

However, Pennetta's upset win against Halep was overshadowed by the huge victory scored by Vinci against Williams, who was expected to run away with an easy straight-set win. In fact, Williams was reportedly a 300-1 favorite on most betting websites heading into the game.

Vinci leaned on her superb control and volleys to escape with a 2-6, 6-4, 6-4 win over Williams in the semis, ending Serena's bid to win all four Grand Slam titles this year and her fourth consecutive title at Flushing Meadows.

After the match, Vinci also admitted that she did not expect to win over Williams. As a proof, she said during a post-game press conference that she is actually planning to fly home on Saturday.

That will not happen because she will collide with her good friend in the final. When asked about her upcoming match against Pennetta, Vinci admitted that they will feel a lot of pressure, but she is hoping that she will be able to enjoy playing in her first singles Grand Slam final appearance.

"We know each other for a long time," Vinci said of Pennetta. "I played against her three or four years ago and I lost on the center court. I remember that I was completely scared, like a little bit blocked. I didn't play. I didn't play in that case. So I hope that tomorrow -- of course I will do my best."

To make the moment special for both players, ESPN reported that Italian Premier Matteo Renzi cancelled all his scheduled appointments for Saturday and flew to New York to watch Pennetta and Vinci play in the final, where the first Italian US Open singles winner will be crowned.

Where To Watch & Live Stream

The Vinci-Pennetta match is expected to start shortly after 3 p.m. ET at Arthur Ashe Stadium. Fans can watch the game on ESPN and through online live stream via US Open Live and WatchESPN.