After Naomi Osaka reached the women's semi-finals earlier, Nishikori's win means there is a Japanese man and woman in the last four of a Grand Slam for the first time in the Open Era.
Naomi Osaka of Japan celebrates her win over Lesia Tsurenko of Ukraine in a quarter-final match on day ten of the 2018 U.S. Open tennis tournament at USTA Billie Jean King National Tennis Center.
Only once had Japan had a man and woman reach the quarterfinals of the same major, and Shuzo Matsuoka and Kimiko Date both lost in that round at Wimbledon in 1995.
A tactical switch enabled and a shift in momentum enabled seventh-seeded Cilic to dominate the fourth set, giving up just four points on serve to send the contest into a deciding set.
However Nishikori fought back and took the next two sets before Cilic forced a decider.
The Croat hit two double faults when 4-3 up and handed the Japanese the advantage before slumping in his chair and laughing at himself ironically.
The Japanese sputtered along until earning his first break chance at 2-4 in the second set and was able to convert to get back on serve.
Cilic, who won their final meeting in straight sets, was pushed to the limit this time around with Nishikori extending his dominance to nine wins from 15 meetings.
The No. 21 seed continued his strong season after returning from a wrist injury that forced him to miss the US Open past year and will play either No. 6 seed Novak Djokovic or unseeded John Millman.
"It was really tough, especially at the end".
But a few hours later, Nishikori helped Osaka create an even more incredible slice of history.
Osaka, who lived in her native Japan until she was 3, started playing tennis in NY after her father saw the Williams sisters playing at the French Open in 1999 and made a decision to teach his daughters. At that time I didn't really want to see any matches, because I know if I watched, I wanted to play. Tsurenko had 31 unforced errors to Osaka's 11, and Osaka finished with 12 winners.
Once she did, the 20-year-old Osaka found they had plenty in common.
For Osaka, her victory is the latest milestone in a watershed year for the 20-year-old who won her first WTA Tour title in Indian Wells, Calif., in March.
Now, Osaka is one of those players on TV - and seeing the same experience from the other side is proving to be just as cool.
She won 59 points to just 28 for the unseeded Ukrainian, who knocked off No. 2 seed Caroline Wozniacki in the second round.
But after labouring through the heat in her previous match, Tsurenko said she was sick Wednesday, waking up with a sore throat and not breathing well.
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