British number two Heather Watson beat Donna Vekic 6-2 6-4 to give Great Britain the lead against Croatia in their Fed Cup promotion play-off tie.
The 24-year-old recorded the win over the world number 84 in 80 minutes.
A win for British number one Johanna Konta over world number 37 Ana Konjuh in the next match would seal victory for GB in the best-of-three contest.
Britons Laura Robson and Jocelyn Rae will face Croatia's Konjuh and Darija Jurak in the final doubles rubber.
"As the week has gone on my opponents have been tougher, but I've also been playing better," said Watson.