The trio will play for John McEnroe's Team World in Boston.
Fifteen Grand Slam singles champions are entered in the 2021 US Open field.
World No. 1 Novak Djokovic aims for the calendar Grand Slam and the men's major mark, while his top two rivals try to stop him.
"In times of difficulty, sport isn’t just necessary, it is vital," two-time gold-medal champion writes.
When Megyn Kelly chimed in with social media critics, Naomi Osaka answered back.
Wimbledon semifinalist has two goals for Tokyo Olympics.
"Representing your country in the Olympics is indispensable," says world No. 1.
