Stan Wawrinka of Switzerland hits a forehand against Jannik Sinner of Italy (not pictured) in the first round on day one of the 2019 U.S. Open tennis tournament at USTA Billie Jean King National Tennis Center. Mandatory Credit: Geoff Burke-USA TODAY Sports

Serena Williams of the USA hits to Maria Sharapova of Russia in the first round on day one of the 2019 U.S. Open tennis tournament at USTA Billie Jean King National Tennis Center. Mandatory Credit: Robert Deutsch-USA TODAY Sports.

Marco Trungelliti of Argentina serves to Kei Nishikori of Japan in the first round on day one of the 2019 U.S. Open tennis tournament at USTA Billie Jean King National Tennis Center. Mandatory Credit: Danielle Parhizkaran-USA TODAY Sports

Novak Djokovic of Serbia hits to Roberto Carballes Baena of Spain in the first round on day one of the 2019 U.S. Open tennis tournament at USTA Billie Jean King National Tennis Center. Mandatory Credit: Robert Deutsch-USA TODAY Sports

Juan Ignacio Londero of Argentina hits to Sam Querrey of the United States in the first round on day one of the 2019 U.S. Open tennis tournament at USTA Billie Jean King National Tennis Center. Mandatory Credit: Danielle Parhizkaran-USA TODAY Sports

Maria Sharapova of Russia hits to Serena Williams of the USA in the first round on day one of the 2019 U.S. Open tennis tournament at USTA Billie Jean King National Tennis Center. Mandatory Credit: Robert Deutsch-USA TODAY Sports

Serena Williams of the USA hits to Maria Sharapova of Russia in the first round on day one of the 2019 U.S. Open tennis tournament at USTA Billie Jean King National Tennis Center. Mandatory Credit: Robert Deutsch-USA TODAY Sports

Maria Sharapova of Russia serves against Serena Williams of the United States in a first round match on day one of the 2019 U.S. Open tennis tournament at USTA Billie Jean King National Tennis Center. Mandatory Credit: Jerry Lai-USA TODAY Sports

Misaki Doi of Japan hits a forehand against Madison Keys of the United States (not pictured) in the first round on day one of the 2019 U.S. Open tennis tournament at USTA Billie Jean King National Tennis Center. Mandatory Credit: Geoff Burke-USA TODAY Sports

Juan Ignacio Londero of Argentina hits to Sam Querrey of the United States in the first round on day one of the 2019 U.S. Open tennis tournament at USTA Billie Jean King National Tennis Center. Mandatory Credit: Danielle Parhizkaran-USA TODAY Sports

Roger Federer of Switzerland, left, and Sumit Nagal of India shake hands after their match in the first round on day one of the 2019 U.S. Open tennis tournament at USTA Billie Jean King National Tennis Center. Mandatory Credit: Danielle Parhizkaran-USA TODAY Sports