Defending champion Novak Djokovic saw off Gael Monfils in a bizarre match of fluctuating fortunes to reach his seventh US Open final in New York.
The Serb beat French 10th seed Monfils 6-3 6-2 3-6 6-2 and will face Stan Wawrinka or Kei Nishikori in the final.
Djokovic, 29, had treatment on both shoulders, while Monfils could barely move at times in punishing conditions.
"Humid" is how Djokovic described it. "I think that's all we were thinking about and feeling."
Monfils robustly rejected the notion that he did not give his all, saying: "I think I tried my best.