Johanna Konta fought back from a set down to beat Zarina Diyas and put Great Britain 1-0 ahead in their Fed Cup play-off against Kazakhstan.
The British number one trailed 5-1 in the first set but went on to win 4-6 6-3 6-2 at London's Copper Box Arena.
If Britain win the best-of-five tie they will earn promotion to World Group II for the first time in 26 years.
British number two Katie Boulter faces Kazakh number one Yulia Putintseva in Saturday's second singles rubber.
The two reverse singles and a doubles match will follow on Sunday (from 12:00 BST).