Serena Williams suffered the first singles loss of her Fed Cup career, but the United States overcame Latvia to book their spot in the Finals on Saturday. (More Tennis News)
Trailing 2-0 in Washington, Latvia's fightback started with Jelena Ostapenko's win over Australian Open champion Sofia Kenin.
Williams' unbeaten record in singles was then ended by Anastasija Sevastova, who recorded a shock 7-6 (7-5) 3-6 7-6 (7-4) victory over the 23-time grand slam champion.
But USA moved into April's Fed Cup Finals thanks to Kenin and Bethanie Mattek-Sands, the duo winning the doubles over Ostapenko and Sevastova 6-4 6-0.
Belarus needed a thrilling doubles rubber to overcome the Netherlands 3-2.
Aryna Sabalenka and Aliaksandra Sasnovich edged Kiki Bertens and Demi Schuurs 4-6 6-3 7-6 (10-8).
Russia survived a test against Romania to prevail 3-2, Switzerland claimed a 3-1 success over Canada and Slovakia beat Great Britain 3-1.
Germany swept Brazil aside 4-0, Spain were too strong for Japan 3-1 and Elise Mertens led Belgium past Kazakhstan 3-1.