It means Osaka and Nishikori are the first Japanese players in the Open era to both make the semi-finals at one grand slam.
Japan's previous best was at Wimbledon in 1995, when both Shuzo Matsuoka and Kimiko Date lost in the quarter-finals.
The momentum swung throughout the match with 2014 champion Cilic looking in control when leading 4-2 in the second set before losing six games in a row.
Initially, it looked like the match might follow a similar storyline from 2014 when seventh seeded Cilic took the opening set from a sluggish Nishikori.
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.
It was Cilic who got off to the stronger start, with Nishikori struggling behind his serve, and he led by a set and a break.
The No. 21 seed continued his strong season after returning from a wrist injury that forced him to miss the U.S. Open past year and will play either No. 6 seed Novak Djokovic or unseeded John Millman on Friday.
"I think it's because of Kei", she said, holding her hands apart to show how much bigger Nishikori is in Japan, from where her family moved to NY when she was 3.
Twitter not based on ‘political ideology,’ CEO tells lawmakers
The tech giants say they don't intentionally suppress conservatives, and perhaps that's true. Shares in Twitter plunged 6.2 per cent, while Facebook dropped 2.3 per cent.
India allows state refiners to use Iran tankers, insurance for oil imports
Oman is a principal supplier of oil to China , with the latter buying nearly 90 percent of its exports previous year . Japan has been asking for a waiver from its ally, saying imports of Iranian crude have been recently falling.
New York Yankees acquire Andrew McCutchen in trade with Giants
McCutchen bolsters the Yankees' outfield depth ahead of a playoff push with Aaron Judge still recovering from a fractured wrist. McCutchen is not the first big name player to lose his beard after joining the Yankees, and he won't be the last.
The No. 20 seed continued what's been a largely dominant run through the draw by winning in just 57 minutes, the third time in her five matches she didn't even have to play an hour.
The No. 20 seed moved from Japan to NY at age 3, and her deepest major run is coming at the same tournament she first visited as a child. "My entire body was shaking, but I was really glad I was able to play well today".
On Wednesday, Osaka only needed 12 winners because a whopping 31 of her other points came via unforced errors by Tsurenko.
Osaka was smooth and confident as she won the first set 6-3.
Osaka, who is just 20 years old, is having a terrific 2018 season. "I feel a lot of support, and I'm really grateful about that".
Osaka had consecutive 50-minute matches earlier in the tournament, including a 6-0, 6-0 thrashing of Aliaksandra Sasnovich in the third round.
Keys won all 10 of her service games, saving the only two break points she faced. The second set was taking on a new meaning where the Japanese started off aggressive and earning points, but then Sabalenka chose to correct mistakes she'd made on the first one.