Minsk - Belarus' Aliaksandra Sasnovich battled back from a set down to beat American Sloane Stephens and force a deciding rubber in the Fed Cup final in Minsk on Sunday.
Earlier, CoCo Vandeweghe put the United States 2-1 up by beating teenager Aryna Sabalenka 7-6 (7/5), 6-1.
The world number 87 Sasnovich prevailed 4-6, 6-1, 8-6 in two hours and six minutes to chalk up her second win over Stephens, who has lost all of her six matches since winning the US Open title in September, in as many meetings.
Vandeweghe and Shelby Rogers take on Sasnovich and Sabalenka for the title in a doubles clash later on Sunday.
"It was one of the most tense matches in my life," Sasnovich said.
"I gave everything I have for the win, the god of tennis was on my side today. The support of the crowd helped me to stay concentrated throughout the game. It was a fantastic match."
Both players produced a catalogue of unforced errors in the opening set but the 24-year-old Stephens held on to take it after an early break.
But in the second Stephens, ranked 13th in the world, suddenly ran out of gas allowing Sasnovich to break twice to level at one set all.
In the deciding set, Stephens led 5-2 before Sasnovich, 23, roared back with four straight games before eventually closing it out 8-6.
In Sunday's early match, Sabalenka and Vandeweghe both played with confidence from the start on the hard court at a packed Minsk Chizhovka 8,000-capacity arena, holding their serves until the 11th game when Vandeweghe broke.
But Sabalenka broke back immediately under the watchful gaze of Belarus president Alexander Lukashenko to force a tiebreak, which the 25-year-old American won 7-5.
In the second Sabalenka, who is 78th in the world rankings, lost her nerve, allowing Vandeweghe to break twice for a commanding 5-0 lead minutes before she took the set and the match with an accurate backhand.
"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," Vandeweghe said.
"She did what she's supposed to do and did what I expected her to do - just swing and pray for it to go in and she did. So you just got to recover and keep fighting.
"And then it showed in the second set, she withered when I kept the pressure on her, and then I just closed it out."
On the opening day, Vandeweghe put the USA ahead with a 6-4, 6-4 win over Sasnovich, while Sabalenka beat Stephens 6-3, 3-6, 6-4 to pull the tie level.
Results from the first day of the ATP Tour Finals at London's O2 Arena on Sunday (x denotes seeding):
Group Boris Becker
Roger Federer (SUI x2) bt Jack Sock (USA x8) 6-4, 7-6 (7/4)
Alexander Zverev (GER x3) v Marin Cilic (CRO x5)
Ryan Harrison/Michael Venus (USA/NZL x8) bt Henri Kontinen/John Peers (FIN/AUS x2) 6-4, 7-6 (10/8)
Jean-Julien Rojer/Horia Tecau (NED/ROM x3) v Pierre-Hugues Herbert/Nicolas Mahut (FRA/FRA x6)