The 2009 champion Juan Martin del Potro of Argentina made his second US Open final as defending champion Rafael Nadal retired with two sets down in their semifinal here.

Del Potro will face either Novak Djokovic of Serbia or Japan star Kei Nishikori in Sunday's men's singles final. Del Potro took the first two sets 7-6(3), 6-2 when the world number one Nadal retired due to knee problems during the match on Friday, Xinhua news agency reported.