The US Open celebrates the American Labor Day holiday with a Williams sisters double-feature, both Serena and Venus vying for quarter-final berths in Arthur Ashe stadium.
World number one and top seed Serena Williams takes on Kazakhstan's Yaroslava Shvedova while sixth-seeded Venus faces hard-hitting 10th seed Karolina Pliskova of the Czech Republic.
World number two Andy Murray headlines the night session, seeking a quarter-final berth against Bulgarian Grigor Dimitrov, the 22nd seed.
Murray, the 2012 champion, has reached the round of 16 or better in 23 straight Grand Slam appearances.
His only defeat at this stage since 2010 came at last year's US Open when he fell in four sets to South African Kevin Anderson.
He owns a 6-3 career advantage over Dimitrov, although he lost their most recent meeting in Miami in March.
Lending piquancy to the clash, Dimitrov is now coached by former Murray coach Dani Vallverdu.
"There's going to be a lot of challenges, especially on an occasion like that, against Andy," Dimitrov said. "He's been playing extremely good tennis. He knows what to do. But in the same time, I know what to do, too."
Men's third seed Stan Wawrinka, who saved a match point en route to a five-set victory over Briton Dan Evans in the third round, takes on Ukrainian Illya Marchenko, who reached the last 16 when mercurial Australian Nick Kyrgios retired injured while trailing after three sets.
Sixth-seeded Japanese Kei Nishikori, two years removed from his run to the final at Flushing Meadows, faces the tall task of Croatian Ivo Karlovic, while eighth-seeded Austrian Dominic Thiem has a daunting clash with 2009 champion Juan Martin del Potro, unseeded but clearly gaining steam in his injury comeback.
Nishikori has reached the fourth round or better at all four majors in a single season.
But he'll be up against an in-form Karlovic, who won titles at Newport and Los Cabos in the build-up to the US Open.
Women's fourth seed Agnieszka Radwanska takes on 18-year-old Croatian Ana Konjuh in search of a quarter-final berth in the only Grand Slam in which she's never made the last eight.
She'll be hoping for an easier time against the Croatian teen than she had at Wimbledon, where she had to save three match points to get past her in the second round.
Action kicks off with fifth-seeded Simona Halep taking on 11th-seeded Spaniard Carla Suarez Navarro in what promises to be a tight duel between players who have split their 10 prior meetings 5-5.
(For more sports news and updates, follow Ahram Online Sports on Twitter at @AO_Sports and on Facebook at AhramOnlineSports.)