On the cusp of the second week of the U.S. Open, this is when it starts to get serious for those players who have hopes of glory at Flushing Meadows.
Defending champion Rafael Nadal is one, and he's in action against Nikoloz Basilashvili on Sunday. Elsewhere in the men's draw, the standout match appears to be fifth seed Kevin Anderson and ninth seed Dominic Thiem's meeting.
Serena Williams is set to star in the women's bracket up against Kaia Kanepi. Last year's winner, Sloane Stephens, is also in action. She faces Elise Mertens.
Selected Sunday Schedule
Arthur Ashe Stadium
(1) Rafael Nadal* vs. Nikoloz Basilashvili
Kaia Kanepi vs. (17) Serena Williams*
(3) Sloane Stephens* vs. (15) Elise Mertens
(3) Juan Martin del Potro* vs. (20) Borna Coric
Louis Armstrong Stadium
(9) Dominic Thiem* vs. (5) Kevin Anderson
(18) Ashleigh Barty vs. (8) Karolina Pliskova*
(11) John Isner vs. (25) Milos Raonic*
*Picks to win
TV Info: In the United States, ESPN and the Tennis Channel will provide coverage. For viewers in the UK, Amazon Prime.
Defending Champions in Action on Sunday
After a couple of routine wins in the first two rounds of the tournament, Nadal was given a much sterner test in his outing against Karen Khachanov, eventually recovering from a set down to win in four.
It's the type of challenge that may help Nadal become battle-hardened ahead of the second week of the competition. As such, Basilashvili is likely to face a top seed who is not only focused but in a competitive groove too.
As we can see, courtesy of the competition's Twitter account, relief was etched on Nadal's face after he picked up this big win:
Juan Martin del Potro looks like one of the most likely challengers to Nadal in the men's draw after progressing through his opening three matches without dropping a set.
The third seed has enjoyed a prosperous year and is beginning to reach the levels that saw him triumph at this tournament back in 2009. Borna Coric will provide a much sterner test for Del Potro than he's had so far in this competition, but the former champion is undoubtedly the big favourite.
As tennis commentator David Law noted, Del Potro's thunderous backhand has been a joy to behold at the tournament:
Williams has also been imperious at Flushing Meadows, with her win over sister Venus in the previous round arguably the best she's played since returning to the sport in May.
The six-time U.S. Open champion moved around the court with such freedom, and she was able to pick out some spectacular winners. Per ESPN Stats & Info, it was another landmark accomplishment for the 23-time Grand Slam champion:
Kanepi has performed well, although will surely find Williams too hot to handle when they face off second on Arthur Ashe.
Following that tussle will be defending champion Stephens' match. The American was impressive in her previous outing, beating two-time Grand Slam champion Victoria Azarenka to reach the fourth round. Mertens, who made it to the semi-finals of the Australian Open earlier this year, is enjoying her best-ever U.S. Open run.