Over a year after her last competitive appearance, Serena Williams made her return but suffered defeat alongside sister Venus.
The Fed Cup final went to a deciding doubles rubber, where the United States got the better of Belarus.
There promises to be plenty of drama in Florida and Minsk on Sunday, with both Fed Cup semi-finals in the balance.
Karolina Pliskova and Barbora Strycova led defending champions the Czech Republic into the Fed Cup semi-finals after winning their rubbers on Sunday for an unbeatable 3-1 lead against Spain.
Yannick Noah will skipper his country's Fed Cup and Davis Cup teams in 2017 after Amelie Mauresmo stepped down.
The Netherlands opened-up a shock 2-0 lead over Russia in the Fed Cup on Saturday on the back of a four-hour win for Richel Hogenkamp against Svetlana Kuznetsova in the tournament's longest ever singl