Wawrinka into US Open semis, Murray loses

Japan's Kei Nishikori is into the US Open semi-finals, toppling world No.2 Andy Murray in five sets, while Juan Martin del Potro has lost to Stan Wawrinka.

Japan's Kei Nishikori has stunned Andy Murray in five sets to reach the US Open semi-finals. (AAP)

Swiss third seed Stan Wawrinka has beaten Juan Martin del Potro of Argentina in four sets to advance to the semi-finals of the US Open.

Wawrinka has downed 2009 champion del Potro 7-6 (7-5) 4-6 6-3 6-2 to set up a semi-final showdown with sixth-seeded Kei Nishikori of Japan.

Nishikori, the 2014 runner-up, stunned world No.2 Andy Murray earlier on Wednesday 1-6 6-4 4-6 6-1 7-5.

The other men's semi-final will pit No.1 Novak Djokovic against 10th-seeded Gael Monfils of France.