Nishikori wins Melbourne epic then reveals he almost quit tennis
The 35-year-old dug deep to save two match points in a five-set epic against Brazil's Thiago Monteiro on John Cain Arena and keep him alive for another day.
Nishikori, who reached a career-high four in the world and was a US Open finalist a decade ago, rallied to win 4-6, 6-7 (4/7), 7-5, 6-2, 6-3 in 4hr 6min.
"I almost gave up at match point," said Nishikori, who is on the comeback trail after spending years sidelined by major hip surgery and an ankle injury.
"He was playing very good and was on a roll. But I somehow fought through.
"It was a really tough one," he added. "I tried to stay calm even though I was almost out of the tournament. I tried to fight to the end."
After his injury battles, Nishikori returned to contest his first two Grand Slams last year since the 2021 season, reaching the second round at Roland Garros before retiring with a shoulder problem.
He recovered to play at Wimbledon, losing in the first round, but admitted it had been touch and go whether he would keep going.
"Almost last year because I had my knee and shoulder two years ago, and I almost came back. I got injured again," he said when asked if he had considered quitting.
"I was thinking, if I have maybe another surgery, then I think mentally I'm not able to fight any more."
But he said he still loved to compete.
"I wanted to play (again) in a big stadium like today," he said.
"That was my goal a year ago when I was doing rehab. I still think that I have the chance to play with these top players."
He gave a glimpse of his progress by making his first final in six years at the Hong Kong Open this month.
Nishikori, the first Grand Slam men's singles finalist from Asia at the US Open in 2014, had played eight five-set matches at Melbourne Park before meeting Monteiro and only lost once -- against Roger Federer in 2017.
He has a 29-8 record in five-set matches at tour level.
"I try to think a lot," he said in explaining his ability to pull through in tough matches.
"I think my focus level, it's always high, especially in the last set. Also, is kind of big for me to stay tough until the end."
Now coached by 2002 Australian Open champion Thomas Johansson, he will next play either American 12th seed Tommy Paul or Australia's Chris O'Connell.