Denmark's Holger Rune fought back from a match point down to reach the Japan Open semi-finals after beating Kei Nishikori 3-6, 6-2, 7-5 on Sunday.
Rune, the number six seed, came back from the brink to win four straight games and end the Japanese veteran's challenge in front of a lively crowd in Tokyo.
"It was about getting that first serve, and if I could save that match point I knew that I could put on pressure," said Rune.
"The momentum shifted a little bit. I lifted myself up, I was more positive."
Rune's semi-final opponent will be France's Arthur Fils, who beat defending champion Ben Shelton 7-5, 6-7 (5/7), 7-6 (7/2).
France's Ugo Humbert will face the Czech Republic's Tomas Machac in the other semi-final.
Nishikori, 34, has been plagued by injuries and he returned to Grand Slam competition at the French Open in May after an absence of almost three years.
He has been in inspired form this week and took control of the match early on.
The Dane needed a medical time-out in the third set and he said that "in one moment I thought it was not going to be".
"But I just kept my belief and trusted my fighting spirit, that was really all I could do and I managed to get through," said Rune.
"Definitely one for the books."
Rune is the only seeded player left in the tournament after Fils dispatched number eight Shelton after an epic contest.
The Frenchman had two match points in the second set but Shelton fought back to take it to a decisive third set.
Fils finally put the American away in a tiebreak, with both players looking in physical discomfort.
"The end was a little bit tough but I'm really happy to move forward," said the 20-year-old Fils.
"I fought as well as I could. My coach and my dad told me to fight until the end and we see the result."
Humbert advances
Humbert advanced after his British opponent Jack Draper retired early in the second set.
The 22-year-old Draper earlier this month became the first British man to reach the US Open semi-finals since Andy Murray won the title 12 years ago.
He was looking to build on his success in Tokyo but he needed medical treatment on his upper body late in a first set that Humbert won 7-5.
The Frenchman was leading 2-1 in the second when Draper signalled that he could not continue.
"I feel sorry for him because he was not 100 percent but at least we played an amazing first set with a great level, great intensity," said Humbert.
"I'm just happy to be in the semis."
Draper had not dropped serve in two matches heading into the quarter-finals in Tokyo but Humbert broke him three times in a hard-fought first set.
His semi-final opponent Machac beat American qualifier Alex Michelsen 7-6 (7/2), 6-3 in the day's first quarter-final.
"Everyone is playing so good, the ranking doesn't matter," said Humbert.
"Everyone plays really good, everyone can beat everyone. I just try to take my chance, to play my game, and let's see what happens."