US Open Tennis 2013 Semifinals: Breaking Down Matches with Upset Potential

The 2013 U.S. Open semifinals are set to take place Friday with the women taking the court first, but on both sides of the tourney there are matchups with major upset potential.

On the men's side, No. 2 Rafael Nadal will square off with No. 8 Richard Gasquet, while No. 1 Novak Djokovic will meet upstart No. 9 Stanislas Wawrinka.

In the women's draw, No. 1 Serena Williams will take on No. 5 Li Na and No. 2 Victoria Azarenka will look to avoid an upset at the hands of Flavia Pennetta.

Let's take a look at which of these matches could end with people feeling stunned.

No. 1 Novak Djokovic vs. No. 9 Stanislas Wawrinka

Djokovic has looked unstoppable in Flushing this year, but when digging a bit deeper, his play isn't all that impressive. Sure, he's dominated most of his matches, but Djoker hasn't exactly faced elite competition.

His match with Mikhail Youzhny—the best player he's faced yet—in the quarterfinals ended with Djokovic dropping his first set of the tourney. He didn't win in impressive fashion either as Djokovic committed 45 unforced errors in the match.

Wawrinka has stunned many to get to the position he's in. The Swiss star has had his fair share of issues in this tourney, but he comes into his match with Djokovic playing his best tennis yet.

After all, it took two upset victories over No. 5 Tomas Berdych and No. 3 Andy Murray for Wawrinka to reach the semifinals. It's pretty clear after those two matches that Wawrinka is at the top of his game and is primed to shock the world.

Granted, Djoker is still a huge favorite in this match, but anything less than great play from the No. 1 seed will result in a stunning defeat at the hands of Wawrinka.

No. 2 Victoria Azarenka vs. Flavia Pennetta

The first sign of concern for Azarenka's hopes of winning the 2013 U.S. Open came in her round of 32 match with Alize Cornet. Azarenka dropped the first set only to come storming back to take the last two.

It was more of the same in her match with No. 13 Ana Ivanovic, and her quarterfinal contest with Daniela Hantuchova was a breeze thanks to the Slovak's inability to capitalize on Azarenka's uninspiring play.

Pennetta, on the other hand, has been playing some great tennis against tough opponents all tourney long. Her victims include No. 4 Sara Errani and No. 10 Roberta Vinci, to name a few. Azarenka hasn't come close to beating opponents of that caliber at Arthur Ashe Stadium this year.

The Italian owns the career series between the two, 2-1. But one of those losses for Azarenka was a walkover. In the pair's last real meeting, Pennetta was victorious over her younger counterpart on a hard surface in 2011, so Pennetta is no stranger to beating Azarenka on the very court type they will meet on in the semifinals.