Argentina's Juan Martin del Potro stunned world No. 1 Rafael Nadal 6-2, 6-4 in the semifinals of Shanghai Rolex Masters on Saturday night.

Nadal, who regained the top ranking this week from Novak Djokovic, was overmatched in what is a very rare occurrence.

The 13-time Grand Slam champion's shots seemed to lack their usual speed and accuracy in the loss.