Who Will Serena Play Next?

Well, there you have it! Serena Williams has prevailed in the U.S. Open quarterfinals, defeating her sister Venus, and leaving her just two wins away from a positively historic accomplishment. She's already in rarefied air to begin with, having secured a second ever-elusive, eponymous "Serena Slam" earlier this year. But now, she's on the verge of accomplishing a feat that only three women before her have ever achieved — winning all major four tournaments in a single calendar year. So, who's left standing in her way? Who will Serena Williams play next?

Luckily, the Williams sisters' epic quarterfinal match was the second of the night, so the whole world already knows who'll be standing across the court from her come Thursday night. Although she won't be nearly as familiar a face — it'll be Roberta Vinci of Italy, who prevailed in her match against Frenchwoman Kristina Mladenovic in the early game on Tuesday. Vinci is a pretty inspirational newcomer to this big stage — at 32, she's actually slightly younger than Williams, but it's her first-ever career appearance in a Grand Slam semifinal.\

According to ESPN, Vinci was eager to see which Williams sister won, but she didn't have a preference: "Doesn't matter. I am in the semifinal."

In other words, there will be a tremendous amount riding on the line for both of these women. On Williams' side of things, it's a battle for a tennis immortality. Not that she isn't already an icon of her sport — she's arguably (though if you ask me, inarguably) the greatest woman ever to play the game. And while gender division in pro tennis sadly means we'll never get to see her compete against the men, she's more individually decorated than any man in tennis history, with 21 Grand Slam titles and counting.

Securing a clean sweep of Grand Slams in 2015 wouldn't just make her one of only six players ever to get it done — three of these others are women, to boot — but it'd inch her closer to Margaret Court's all-time career record of 24 Grand Slams, leaving her tied for second place with Steffi Graf, at 22.

On Vinci's end of things, however, there are no epic historical parallels, or further decorations to a legendary career. To the contrary, she's never been this deep into a major tournament, and at 32 — considered well-past-prime for any tennis player not named Serena — she's not likely to get another chance like this.

Basically, this is one of those matches that figures to be thrilling no matter what happens. A loss for Williams would be heartbreaking, but so too would Vinci getting bounced from her best-ever shot at a major tournament win. In short, you're likely to see both women playing with maximum desire, and it figures to be can't-miss entertainment. The match is scheduled for Thursday night at 7 p.m. ET, so be sure to clear your evening.