Rafael Nadal, of Spain, returns a shot to Jack Sock, of the United States, at the Citi Open tennis tournament Wednesday, Aug. 4, 2021, in Washington. (AP Photo/Nick Wass)

Rafael Nadal, of Spain, reaches for a shot from Jack Sock, of the United States, at the Citi Open tennis tournament Wednesday, Aug. 4, 2021, in Washington. (AP Photo/Nick Wass)

Jack Sock, of the United States, returns a shot to Rafael Nadal, of Spain, at the Citi Open tennis tournament Wednesday, Aug. 4, 2021, in Washington. (AP Photo/Nick Wass)

Jack Sock, of the United States, hits a forehand to Rafael Nadal, of Spain, at the Citi Open tennis tournament Wednesday, Aug. 4, 2021, in Washington. (AP Photo/Nick Wass)

Rafael Nadal, of Spain, reacts during a match against Jack Sock, of the United States, at the Citi Open tennis tournament Wednesday, Aug. 4, 2021, in Washington. (AP Photo/Nick Wass)

Rafael Nadal, of Spain, reacts during a match against Jack Sock at the Citi Open tennis tournament Wednesday, Aug. 4, 2021, in Washington. (AP Photo/Nick Wass)

Jack Sock, of the United States, waves to the crowd after a loss to Rafael Nadal, of Spain, in the Citi Open tennis tournament Wednesday, Aug. 4, 2021, in Washington. (AP Photo/Nick Wass)

Rafael Nadal, of Spain, reacts during a match against Jack Sock, of the United States, in the Citi Open tennis tournament Wednesday, Aug. 4, 2021, in Washington. (AP Photo/Nick Wass)

Rafael Nadal, of Spain, reacts to the crowd after he defeated Jack Sock, of the United States, at the Citi Open tennis tournament Wednesday, Aug. 4, 2021, in Washington. (AP Photo/Nick Wass)