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.