Germany's Alexander Zverev reached his first Grand Slam final in the most difficult manner after fighting back to beat Spain's Pablo Carreno Busta in a tense US Open five-setter.
Fifth seed Zverev, 23, looked lost as Carreno Busta played smartly and precisely to race into a two-set lead.
But Zverev showed incredible resolve to turn the match around and win 3-6 2-6 6-3 6-4 6-3 against the 20th seed.
Zverev will play Dominic Thiem or Daniil Medvedev in Sunday's final.
Austrian second seed Thiem, 27, faces Russian third seed Medvedev - who lost to Spain's Rafael Nadal in last year's final - in Friday's second semi-final at Flushing Meadows.
The final on Sunday will see a new Grand Slam champion crowned for the first time since the 2014 US Open when Croatia's Marin Cilic won.
The absence of Nadal and Switzerland's Roger Federer at the behind-closed-doors Grand Slam, plus the expulsion of Serb top seed Novak Djokovic for hitting a line judge with a ball, has given the chance for a new name to be etched onto a major trophy.
Switzerland's Stan Wawrinka was the last man outside of the 'Big Three' to win either the Australian Open, French Open, Wimbledon or US Open, following his win at Flushing Meadows in 2016.
The chances of Zverev becoming the newest Grand Slam champion looked slim after Carreno Busta's strong start.
But the former world number three is now one win away after a remarkable comeback in a semi-final which was neither high-quality or engrossing.
The German grinned incredulously as he waved his fists towards his box when Carreno Busta lamped a return into the net on the second match point.
"I knew I had to come up with better tennis and be more stable," said a relieved Zverev.
"I knew I had to play better, I've never come back from two sets to love but I'm happy to do it at this stage.
"I'm through to my first Grand Slam final and that's all that matters."