Great Britain trail 2-1 in their Fed Cup World Group II play-off in Romania after Simona Halep beat Johanna Konta in Sunday's opening match.
The hosts were without captain Ilie Nastase after he was banned on Saturday for swearing at the umpire, Konta and her captain Anne Keothavong.
Halep seemed unaffected as she beat Konta 6-1 6-3 in impressive style.
GB will lose the tie if Heather Watson is beaten by Irina-Camelia Begu in the next match before the doubles rubber.
Konta was left in tears after Nastase's conduct and, even though the world number seven still beat Sorana Cirstea on Saturday, she found Halep, ranked five in the world, a tougher test.
Halep raced into a 4-0 lead as she made the most of her clay-court knowhow and broke to love in taking the first set in 27 minutes.
Konta gave signs of a comeback by breaking Halep and taking a 3-1 lead in the second set but Halep responded by taking five games in a row to win the match.