Late Tuesday afternoon, Roberta Vinci sat with a smile, elated that after a pro career that began in 1998 and a Grand Slam journey that began in 2002, she finally has reached the semifinals of one of tennis' major events.

And it was completely OK that her opponent in the U.S. Open semifinals Thursday night will be Serena Williams, who beat her sister Venus Tuesday night.

The 32-year-old Italian, whose best Grand Slam results have been the four doubles titles won with partner Sara Errani, earned her spot in the heat of Tuesday afternoon on Arthur Ashe Stadium court, beating the struggling Kristina Mladenovic of France, 6-3, 5-7, 6-4.

Vinci wouldn't know until later in the evening which Williams sister she would play, but said she didn't care.

"It doesn't matter if Serena or Venus," she said. "I'm so happy. I would like to enjoy my semifinal on Thursday. I did not expect one semifinal at the U.S. Open, so I'm really happy. Now I enjoy my day. Tomorrow rest and play my game on Thursday."

Vinci had reached the quarterfinals of the Open two other times. Each time she lost to a countrywoman, Errani in 2012 and Flavia Pennetta in 2013. She once reached No. 11 in the world, but her ranking has fallen to 43rd as her career winds down.

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She is an unlikely candidate for a semifinal berth, though chaos in her quarter of the draw helped. Seeded players Jelena Jankovic and Carla Suarez Navarro were eliminated early. Eugenie Bouchard, who was to be her opponent in the fourth round, had to withdraw after a training room accident that left her with a concussion, giving Vinci a free pass to the quarters. With Mladenovic ranked 40th, Vinci hasn't faced one seeded player in four matches.

Vinci has never beaten a Williams sister, losing four times to Serena and three times to Venus. The semifinal punctuates a career in which she won nine singles titles.

"I think I am at the end of my career, so my first semifinal, it's incredible," Vinci said. "I'm very proud of myself."