The top two men aim to set up their second final in two weeks and sixth meeting of 2013.  But both Rafael Nadal and Novak Djokovic face dangerous opponents in the Shanghai semifinals.

Novak Djokovic vs. Jo-Wilfried Tsonga

In the first semifinal Saturday, Novak Djokovic will be attempting to propel himself one step closer to defending his ATP crown in Shanghai. When he last faced this opponent in Shanghai, Tsonga won in three sets. This match came in the round-robin phase of the ATP year-end championships, now known as the World Tour Finals after moving from Shanghai to London.

Tsonga last defeated Djokovic in a five-set quarterfinal at the 2010 Australian Open, before the Serb’s emergence as a perennial contender. Since that meeting, Djokovic has won their last eight matches and has not dropped a set in their last four. Thus, he leads the overall head to head 10-5.

With Andy Murray’s withdrawal from the World Tour Finals, Tsonga stands in the virtual eighth qualifying spot for London and looms only 135 points behind Roger Federer for the seventh spot.

Djokovic comes into this match after a tightly contested victory over another Frenchman, Gael Monfils, while Tsonga easily dispatched unseeded German Florian Mayer to reach the semifinals. He missed the US Open due to a knee injury and lost in the finals of Metz to Gilles Simon, so he will be happy to have regained form at such a critical juncture of the year.

Unfortunately for Tsonga, the matchup is a quite a difficult one. Djokovic’s strongest shot, his backhand, can be safely struck cross-court into Tsonga’s backhand, among the weakest shots in the top ten. To make matters even more complicated for Tsonga, Djokovic’s defense and return game work to effectively blunt Tsonga’s offensive weaponry.

Interestingly, Djokovic has a 1-4 record against the Frenchman on indoor hard courts, so Tsonga would welcome some rain tomorrow. While he might trouble the world No. 2 at times, he should lack the consistency to win two sets from Djokovic.

Prediction: Djokovic in two sets

Rafael Nadal (Spain) vs. Juan Martin Del Potro (Argentina)

The second and probably more competitive semifinal reprises the men’s final at Indian Wells this year. Having defeated Andy Murray and Novak Djokovic in the quarterfinals and semifinals there, Del Potro almost pulled off the trifecta but was denied by Nadal in a three-set battle.

Victorious in nine of their 12 meetings, Nadal has won four straight from Del Potro since they squared off in a 2009 semifinal at the US Open.  In each of their last three meetings, though, Del Potro won a set from Nadal but could not seal the deal.

Each man seeks his second final in as many weeks, Nadal having finished runner-up in Beijing and Del Potro having claimed the Tokyo title. In addition, with a victory over Nadal tomorrow, Del Potro would guarantee his qualification for the World Tour Finals.

Nadal has defeated every member of the current top 10 this year other than Andy Murray, whom he has not played, and will be looking to improve upon his astonishing 18-2 record in that category. But Del Potro matches up well to Nadal, compared with most of his rivals.

The Argentine’s wingspan allows him to contain Nadal’s lefty serves to his backhand. Once engaged in a rally, moreover, Del Potro’s height mitigates the effectiveness of Nadal’s heavy topspin forehand. The Argentine will not play as many balls at chest level as a player of more ordinary stature would.

Another aspect of Del Potro’s game that will trouble Nadal, especially on the extremely quick Shanghai surface, is his sheer firepower that can hit anyone off a court. Other than Fernando Gonzalez, few men have hit forehands harder than Del Potro does. The former US Open champion can deploy his magnificent running forehand to counter Nadal’s down-the-line forehand, making it more difficult for the Spaniard to finish points with that stroke.

While Nadal has not lost a set this week, Del Potro should have a reasonable chance to score the upset and reach his second Masters 1000 final of the season.

Prediction: Del Potro in three sets