Eventually, the physically demanding action proved too much for a fading Andy Murray, and Novak Djokovic pulled away to reach the semifinals for the eighth consecutive year.
After a bad-as-can-be start, dropping the first three games, Serena Williams quickly turned things around and stretched her U.S. Open winning streak to 19 matches to get back to the semifinals.
The match went 4 hours, 15 minutes, and the 10th-seeded Nishikori managed to shake off any lingering exhaustion from his previous victory, which lasted 4:19 and ended at 2:26 a.m. Tuesday, equaling the latest finish in tournament history.
Andy Murray went more than a year between victories over top-10 opponents. Now he needs to make it two in a row.
Ivanovic, who had been having her best season since winning the French Open in 2008, lost to Karolina Pliskova 7-5, 6-4 in the second round Thursday.
Top-ranked Serena Williams is seeded No. 1 as she seeks her third straight U.S. Open title.
Dealing with adversity in intense matches is where Serena Williams has shown the biggest improvement. As her sister Venus said, “the only player that can beat Serena is Serena herself.”
American Serena Williams captured her second straight US Open title over Victoria Azarenka in a repeat of last year’s final.
Rafael Nadal is in the US Open final after victory Saturday over Richard Gasquet.
Six times, Serena Williams was a single point from winning on Friday. Six times, she failed to come through. All that did, of course, was delay the inevitable.
Flavia Pennetta made her first Grand Slam semifinal, defeating 10th-seeded Roberta Vinci 6-4, 6-1 on Wednesday in an all-Italian quarterfinal at the US Open.
No. 2 Victoria Azarenka rallied from a set down for the second straight match, beating Ana Ivanovic to return to the US Open quarterfinals.
Roberta Vinci has reached the US Open quarterfinals for the second straight year, beating fellow Italian Camila Giorgi.
After the match, Victoria Azarenka said of the call: “That was the most ridiculous thing there is.”
Only a few spots separate them in the seedings. Still, the considerable gulf between No. 1 Serena Williams and No. 4 Sara Errani was hard to ignore in their matches Thursday at the U.S. Open.