Britain's Heather Watson was unable to earn her first WTA Tour main-draw win since September as she lost to Russian teenager Anastasia Potapova at the Hungarian Open.
Watson, 26, lost 6-4 2-6 7-6 (7-4) against the 17-year-old in Budapest.
Watson, who has dropped to 111th in the world, led 5-3 in the final set before Potapova won the next three games.
The Briton broke serve to force a tie-break, but 87th-ranked Potapova quickly took control in the decider.
Potapova, who has reached the final in two of the seven main-draw tournaments she has played, sealed victory with an ace on her first match point.
Watson grew frustrated in the latter stages of a tense, two-hour contest, often throwing her racquet onto the court and sitting on her chair with her heads in her hands at one changeover, as the possibility of a first main-draw win since reaching the Quebec City semi-finals slipped away.
It was her first appearance since missing Great Britain's Fed Cup matches earlier this month through illness.
Her only victories this year have come in qualifying at the Hobart Open, while she also won matches in Challenger and ITF Tour events - the tiers below the main WTA Tour - towards the end of last year.