Johanna Konta battled through tiredness to send Great Britain into April's Fed Cup promotion play-offs, with her win over Aleksandra Krunic sealing victory over Serbia.
Konta, seen lying on the floor in the gangway before the start of the third set, needed to be helped to her feet at the end of her 7-6 (7-1) 3-6 6-2 win.
Her team-mate Katie Boulter had earlier dismissed Ivana Jorovic 6-4 6-3.
GB are one win away from reaching World Group II for the first time since 1993.
More to follow.