Teenager Aryna Sabalenka left the Fed Cup final in the balance by beating Sloane Stephens to bring Belarus level after CoCo Vandeweghe struck the first blow for United States in Minsk on Sunday (AEDT).

The No.78 ranked Sabalenka beat out-of-sorts US Open champion Stephens 6-3 3-6 6-4 in the second rubber to make it one apiece.

Belarus's hopes of winning a first Fed Cup title were dealt a blow when Victoria Azarenka ruled herself out of the showdown because of an ongoing custody dispute with her baby's father, but Sabalenka stepped up in her absence.

The 19-year-old Belarus No.1 racked up 57 unforced errors, but also came up with 31 winners to get the Chizhovka Arena rocking.

Sabalenka claimed the decisive seventh break in a tense final set to seal the victory and will now turn her attention to taking on Vandeweghe in the opening match.

Vandeweghe earlier put United States ahead with a 6-4 6-4 win over Aliaksandra Sasnovich.

World No.10 Vandeweghe went into the opening rubber with a perfect singles record in the competition this year and was too good for Sasnovich, giving her country the upper hand as they attempt to end a 17-year-wait for a Fed Cup triumph.

Vandeweghe, a grand slam semi-finalist in Australia and at Flushing Meadows this year, broke in the first game of the match and three times in the second set to secure the first point.