Del Potro, the 2009 US Open champion, beat reigning US Open champion Murray for just the second time in seven meetings and booked a clash with World No 1 Novak Djokovic for a place in the final.
Djokovic earlier remained unbeaten in 2013 with a 6-3, 6-1 victory over France’s Jo-Wilfried Tsonga. The defeat means Murray will have to wait longer for a chance to overtake Roger Federer for the second spot in the world rankings.
Murray could have risen to No 2 for the second time in his career by reaching the final here after Federer bowed out in the quarter-finals. But the Scot was undone by eight double faults, the last coming on match point to bring things to a close after two hours and 32 minutes.
Sharapova in women’s final
Maria Sharapova reached her first final of 2013 on Friday, beating Maria Kirilenko 6-4, 6-3 in a semi-final slugfest to set up a title showdown with Caroline Wozniacki. By reaching the final, Sharapova is projected to rise one spot to No 2 in the world when the new rankings are announced on Monday.