A knee injury forced defending champion Rafael Nadal to quit his men's singled semi-final match against Juan Martin del Potro at the 2018 US Open early Saturday morning.
Later, two-time champion Novak Djokovic beat Kei Nishikori in straights sets to enter his eighth final at the Flushing Meadows.
Nadal, who played two five-set matches in the previous rounds, struggled with fitness. The Spaniard needed medical attention to have his right knee bandaged before quitting. He was trailing 7-6(3), 6-2.
Del Potro, however, played brilliant tennis to dominate the world number one before it came to an abrupt halt. In the match lasting just under two hours, the Argentine countered Nadal with a disciplined performance replete with huge ground strokes.
Third seed Del Potro, who won the title in 2009, will play former world number Djokovic in the final.
Djokovic, who won the tournament in 2011 and 2015, beat Japan's Kei Nishikori 6-3, 6-4, 6-2 to enter his 23rd Grand Slam final.
In a replay of their 2014 semi-final which was won by the Japanese, Djokovic broke Nishikori four times to complete a comfortable win in two hours and 22 minutes.
Djokovic, 31, will start as the favourite in Sunday's final. He leads del Potro 14-4 in their 10-year rivalry, including two wins without dropping a set at the US Open in 2007 and 2012.
A win will help Djokovic equal American great Pete Sampras on the all-time list, with 14 Slam titles.
Meanwhile, first time finalist and history making Naomi Osaka of Japan will take on American legend Serena Williams for the women's singles crown.