The top two men face a pair of unexpected challengers as they look to set up their third US Open final in four years.  Nick Nemeroff analyzes what to expect from favorites and underdogs in Saturday's semifinals.

Novak Djokovic (Serbia) vs. Stanislas Wawrinka (Switzerland)

If this US Open semifinal is even half as competitive and entertaining as the Australian Open fourth-round match that these two contested back in January, the fans at Arthur Ashe will definitely get their money’s worth.  In what was by far Djokovic’s most laborious test on his way to his fourth Australian Open title, the Serbian took out Wawrinka 12-10 in the fifth set of a match that lasted five hours and two minutes.

Wawrinka’s losing streak against Djokovic has lasted since 2006, when the Serb was a teenager. The two warriors have played 11 matches on three different surfaces in seven years since then, but Stan has not yet found the recipe to success. What he has found, which was clearly demonstrated in his quarterfinal thrashing of 2012 champion Andy Murray, is a killer instinct. 

In 2013, Wawrinka has reached the final at the Masters 1000 tournament in Madrid and the quarterfinals of Roland Garros. He has recorded wins over Murray, David Ferrer, Tomas Berdych, Jo-Wilfried Tsonga, and Nicolas Almagro.

Against Djokovic, Stan’s ability to embrace the defining moments in matches will loom large. He was utterly relentless in his attack of Murray in their quarterfinal match. He smelled blood and knew he was facing a weakened and edgy Murray, and he took full advantage.

While Djokovic’s game is certainly stronger than Murray’s game at the moment, the plan for Wawrinka should remain the same. He needs to seize any opportunity to take the initiative. Balls that he might not attack audaciously must be attacked with audacity in this match.

The middle of the court is where Wawrinka needs to do the majority of his work throughout this contest.  If Djokovic can dictate and drive Stan from side to side instead, he will dominate the rallies.

Any type of offensive strategy will be Wawrinka’s friend in this match. Taking his groundstrokes (especially the backhand) up the line, serving and volleying, upping the ante on second serves, and flattening out shots early in the rally will all be key for Wawrinka. Meanwhile, the backhand-to backhand exchanges in this duel promise to be exquisite as arguably the best one-handed backhand and the best two-handed backhand in the ATP lock horns.

At the end of the day, Stan will need to get on and off the court in a hurry if he expects to win this match. If the match stretches to four or five sets, Novak should hold the edge. It will be very difficult, although he did it in Australia, for Wawrinka to maintain stellar aggressive tennis over four or five sets.

Prediction: Djokovic in four sets

Richard Gasquet (France) vs. Rafael Nadal (Spain)

For Richard Gasquet, talent has never been a question. The question that had been asked for a while, and had seemed to be unequivocally answered, was whether or not the Frenchman could transform his unique talent into production on the court worthy of his skill set. The answer of course has been no.

Gasquet’s record in the fourth round of majors coming into the 2013 US Open was 1-15. His only win in the fourth round of a major came at Wimbledon 2007. This enduring inability to perform when it really counts has overshadowed and detracted from the impressive components of Gasquet’s game—until now.

On his way to the semifinals, Gasquet saved a match point and rallied from two sets to one down against Milos Raonic before taking out David Ferrer in five sets after letting a two-set lead slip away. The mental resilience that pushed Gasquet through these psychologically demanding contests must be in full force against his semifinal foe, the ultimate mental giant, Rafael Nadal.

Nadal owns a 10-0 record against his French nemesis and has not dropped a single set in their head to head since 2008. Thus, the task would seem to be nearly impossible for Gasquet to complete. He must find a way to win not only one but three sets from a man who has not let him see the light of day for nearly half a decade.

Gasquet’s one-handed backhand is one of the most aesthetically graceful and pleasing shots in the world. His tremendous amount of racket head speed and high take back should allow him to better handle the vicious Nadal topspin forehand.  But one tendency that Gasquet must absolutely avoid during this match is his deep court positioning. The Frenchman loves camping out well behind the baseline and throwing heavy topspin shots at his opponents. He must recognize that defensive tennis will not succeed in this matchup.

That remarkable one-handed backhand will prove ineffective if it is consistently struck from the Central time zone. Gasquet must take a page out of Philipp Kohlschreiber’s book and hug the baseline in order to take his backhand flat and early. 

Other tactical ploys that Gasquet can integrate all involve mitigating Nadal’s penetration of his backhand side. Look for the Frenchman to move closer to the center of the court when returning on the deuce side and closer to the doubles alley when returning on the ad side, which would help him cut off Nadal’s lethal lefty serve.

Gasquet also should take any Nadal forehand up the line unless it stretches him out of position or pushes him further behind the baseline. The more backhands that Nadal is hitting, the better. And, if he finds himself unable to redirect Nadal’s heavy balls up the line, it would be wise for him to throw in some underspin backhands in an attempt to exploit Nadal’s extreme grip.

Above all, to underscore my earlier point, Gasquet cannot lose the battle of court positioning. He certainly is not guaranteed to win the match if he wins that battle, but he will lose in straight sets if he does not.

Prediction: Nadal in three sets