NEW YORK (AP) — The Latest on the U.S. Open tennis tournament (all times local):
Novak Djokovic is about to try to do his part to set up a U.S. Open quarterfinal against Roger Federer.
Djokovic is warming up for his fourth-round match against Joao Sousa of Portugal in Arthur Ashe Stadium.
The winner of Djokovic vs. Sousa will face either Federer or John Millman of Australia next.
Kei Nishikori is into the quarterfinals of his return to the U.S. Open.
The 2014 runner-up in Flushing Meadows beat Philipp Kohlschreiber 6-3, 6-2, 7-5 to reach the final eight in his second straight Grand Slam tournament.
Nishikori missed the U.S. Open last year because of a right wrist injury. The No. 21 seed from Japan returned to the tour early this year, building his confidence back with a victory in a Challenger Tour event, then reached the final in Monte Carlo and the quarterfinals at Wimbledon, where he lost to eventual champion Novak Djokovic.
He will next face either No. 7 seed Marin Cilic — who beat him in the 2014 U.S. Open final — or No. 10 David Goffin.
Kohlschreiber was denied again in his fifth attempt to win a fourth-round match at the U.S. Open. The German reached his lone Grand Slam quarterfinal at Wimbledon in 2012.
Madison Keys returned to the U.S. Open quarterfinals with a 6-1, 6-3 victory over No. 29 seed Dominika Cibulkova of Slovakia.
Keys was an Open finalist a year ago and lost to Sloane Stephens. She lost to Stephens again this year in the French Open semifinals.
The 14th-seeded Keys will play the winner of the Carla Suarez Navarro vs. Maria Sharapova match in the night session at Arthur Ashe Stadium.
Keys has reached at least the quarterfinals in three of the four Grand Slam tournaments this year. She had six aces and no double-faults Monday in perhaps her best performance of the tournament.
The extreme heat policy is back in effect at the U.S. Open.
A 10-minute break will be allowed between the second and third sets of women's singles matches if either player requests one. For men's singles matches, the break would come between the third and fourth sets.
The policy is a rule on the women's tour but not the men's. U.S. Open officials began putting it in play last week, when temperatures first soared into the mid-90s. The policy was in place Tuesday through Thursday.
It was 87 degrees just before the start of Monday's day session on Arthur Ashe Stadium.
The U.S. Open is getting closer to a Roger Federer-Novak Djokovic quarterfinal showdown.
Both play unseeded opponents in the round of 16 Monday at Arthur Ashe Stadium. Federer is a five-time U.S. Open champion and Djokovic has won the tournament twice. Djokovic is 27-0 in the U.S. Open against players ranked outside the top 50.
Federer, the No. 2 seed, faces 55th-ranked John Millman. Djokovic, the No. 6 seed, takes on 68th-ranked Joao Sousa. Neither Millman nor Sousa has reached the final eight at a Grand Slam tournament.
There are two other big matches at Ashe when 2006 champion Maria Sharapova plays No. 30 Carla Suarez Navarro, and 2017 runner-up Madison Keys takes on No. 29 Dominika Cibulkova.
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