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.
Federer was broken only once, part of a three-game run for Bautista Agut that took the score from 5-1 to 5-4. But Federer had no trouble the second time he tried to serve out that set, which he ended with a pair of aces.
Colorful Gael Monfils is back in the US Open quarterfinals.
Gael Monfils beat Grigor Dmitrov 7-5, 7-6 (6), 7-5 on Tuesday to reach the quarterfinals of the U.S. Open for the first time since 2010.
Murray-Djokovic feels much more like a Grand Slam title match than a quarterfinal, and for good reason.
Australian Open champ Stan Wawrinka tumbled into the stands, kept calling for the trainer, and still pulled away to reach the U.S. Open quarterfinals.
Serena Williams reached her first Grand Slam quarterfinal of the year with a 6-3, 6-3 victory over Kaia Kenepi in the U.S. Open on Monday, keeping her hopes alive for a third straight Flushing Meadows crown.
The top seeds made it look easy on a hot and humid Labor Day.
Djokovic, the 2011 champion at Flushing Meadows, made only 19 unforced errors, saved both break points he faced, and breezed past 22nd-seeded Philipp Kohlschreiber of Germany 6-1, 7-5, 6-4 Monday.
Bellis played on the grandstand court, Flushing Meadows’ third-largest venue, to accommodate her following after her performance in the main draw.
The second-seeded Federer was a game from losing the first set to Marcel Granollers in the third round Sunday when play was stopped because of lightning.
The sisters are bidding for their 14th Grand Slam doubles title, but first at Flushing Meadows since 2009.
10th seed Caroline Wozniacki dazzled on the Ashe Stadium Court in the third set, beating 5th seed and 2014 French Open champ Maria Sharapova 6-4, 2-6, 6-2 to advance to the quarterfinals.
Wozniacki beat the five-time major champ 6-4, 2-6, 6-2 in 2 hours, 37 minutes on a steamy Sunday.