It was odd enough to see a player be allowed to do that during, instead of after, a set, but even odder for it to happen after an even number of games, rather than at an odd-game changeover.
Cilic won the first set 6-2 but Nishikori fought back to win the next two 6-4 7-6.
There was a subdued atmosphere on Arthur Ashe Stadium with the crowd struggling to get into the match.
The only previous time the pair had played had been in the very different environs of the 2014 ITF $25,000 event in Irapuato, Mexico; back then, a 16-year-old Osaka had taken the match 6-4, 6-3. He will play either No. 6 seed Novak Djokovic or unseeded John Millman on Friday.
Keys, who at 14 is the highest seed left in the women's draw, has shown a determination to go one step further than a year ago, having only dropped one set through her four matches.
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The rupee, which lost 10 paise against the U.S. dollar in late afternoon trade on Monday, ended at a new record low of 71.10. This came at a time when India's crude oil imports from Iran had increased by 52 percent in June 2018.
And it is also the first time a Japanese man and woman have made the semi-finals of the same Grand Slam after Naomi Osaka won her quarter-final earlier today.
Newly minted U.S. Open semifinalist Naomi Osaka grew up on Long Island until she was 9, but tennis fans wouldn't be able to tell that by simply watching her on the court.
Kei Nishikori defeated Marin Cilic in a five-set marathon in the U.S Open quarter-finals on Wednesday.
After Cilic evened the match by taking the fourth following a 10-minute break for heat, Nishikori was on the verge with running away with the fifth, holding a break point for a 5-1 lead.
Osaka was an easy victor in her quarterfinal, eliminating unseeded Lesia Tsurenko of Ukraine 6-1, 6-1 in all of 57 minutes.
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He likened it to another controversial, landmark Supreme Court decision, the Miranda ruling about the rights of criminal suspects. Judge Kavanaugh had dissented when, in 2011, his court upheld new restrictions on assault weapons in the District of Columbia.
The 20-year-old Osaka is the first Japanese woman to make the last-four of any Slam since Kimiko Date at Wimbledon in 1996 - a year before she was born. Tsurenko had 31 unforced errors to Osaka's 11, and Osaka finished with 12 winners.
Osaka quelled nerves in her quarterfinal appearance to put in an assured performance, only dropping a handful of points on her serve. So far in this Open, she's held opponents scoreless in three sets, and she's dropped only one set thus far. She won the Indian Wells Open and made it to the fourth round of the Australian Open.
Keys punched her ticket with a victory over Carla Suarez Navarro on Wednesday.
Serbian sixth seed Djokovic, who will cap the night session, is in familiar territory, appearing in his 11th quarter-final at Flushing Meadows, and looks like a favourite with five-times victor Roger Federer knocked out of his half of the draw.
Keys was the runner-up to Sloane Stephens at the U.S. Open in 2017, then lost to Stephens in the French Open semifinals this year.
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Naturally, Dorsey said Twitter doesn't "feel great about this", and that the company can't use its scale as an excuse. The afternoon hearing before the House Energy and Commerce Committee was to focus on bias and Twitter's algorithms.