Rafael Nadal is seeded No 1 at the US Open for the first time since 2010.
Karolina Pliskova is making her debut as the top-seeded woman at any Grand Slam tournament.
The US Tennis Association announced the seedings Thursday, strictly adhering to this week's ATP and WTA rankings.
The US Open draw is Friday; play begins Monday.
Nadal returned this week to No 1, a ranking he last held in 2014. That year's French Open was the last time the Spaniard was seeded No 1 at any major.
The man Nadal replaced atop the ATP, Andy Murray, is seeded No 2 at Flushing Meadows, with Roger Federer No 3.
Alexander Zverev is No 4, and 2014 US Open champion Marin Cilic is No 5.
After 2016 US Open runner-up Pliskova, Simona Halep is the women's No 2 seed, followed by Wimbledon champion Garbine Muguruza at No 3. Defending champion Angelique Kerber is No 6.
Radwanska in S/F
NEW HAVEN: Top-seeded defending champion Agnieszka Radwanska of Poland beat eighth-seeded Shuai Peng of China 7-5, 6-3 on Thursday night to reach the Connecticut Open semifinals.
"She's definitely a tough opponent," Radwanska said. "I've played her a few times before so I knew what I had to do. I really pushed myself even more than 100 percent today."
Seeking her first title of the year and 21st overall, Radwanska will face Australia's Daria Gavrilova on Friday in the US Open tuneup event at The Connecticut Tennis Center at Yale. "Playing someone for the first time is very challenging, but also very exciting after so many years on the tour playing the same players," Radwanska said. "It's very nice to play someone for the first time."
Gavrilova beat Belgium's Kirsten Flipkens 6-2, 6-4.
"The plan was to be aggressive. She's a very tricky player," Gavrilova said. "It feels pretty good right now. I'm really happy with the way my tournament is going."
Second-seeded Dominika Cibulkova of Slovakia and Elise Mertens of Belgium also advanced.
Cibulkova beat sixth-seeded Anastasia Pavlyuchenkova of Russia 7-5, 6-4, and Mertens advanced when China's Zhang Shuai withdrew because of a right arm injury.
Cibulkova raced to a 5-0 lead in the second set, then needed five games to finish off Pavlyuchenkova.
"She made it extremely tough for me in the end," Cibulkova said. "I was playing very well in the whole second set, but then she started playing even better. I had four match points, and she hit an ace every time so I couldn't do much about it. But I just kept fighting and I said to myself, 'OK, this one's going to be yours.'"