The United States moved one win away from winning the Fed Cup final after Coco Vandeweghe turned in another calm display to beat Belarus's world number 78 Aryna Sabalenka 7-6(5) 6-1 on Sunday.
The U.S., who are seeking a record-extending 18th title, lead Belarus 2-1 with two rubbers remaining.
U.S. Open champion Sloane Stephens can clinch a first Fed Cup title in 17 years for the U.S. team when she takes on 87th-ranked Aliaksandra Sasnovich in Sunday's second reverse singles.
Vandeweghe, who beat Sasnovich on Saturday before Sabalenka stunned Stephens, came from behind to win a first set tie-break on Sunday before breezing through the second set.
"I know she (Sabalenka) has only got one style of play and she's just going to keep swinging," Vandeweghe said.
"I knew if I just kept giving myself opportunities and getting my nose in front in her service games I'd keep getting opportunities and she'd eventually break down."
The American is the first player to record a spotless year in Fed Cup singles rubbers since Petra Kvitova went unbeaten for Czech Republic in 2011.
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