Britain's Francesca Jones missed two match points in a narrow defeat by Talia Gibson in the Nottingham Open first round.
Jones battled back from a set and a break down - and a medical timeout - to force a deciding set against Australia's Gibson.
After being an early break down in the third, Jones hit back and held two match points as she served for victory at 5-3.
However, world number 66 Gibson broke back and held firm in the resulting tie-break to win 6-3 5-7 7-6 (7-4) after a gruelling three hours and six minutes.
Jones showed good fight in what was the longest match of her career, hitting 15 aces and landing 75% of her first serves.
She also twice appeared in discomfort, particularly after being broken to start the second set when she sat with her head under a towel, breathing deeply.
The doctor was called to court to check her blood pressure and vitals and Jones continued, breaking Gibson back before eventually taking a tight second set.
The 25-year-old took another medical timeout at 5-5 in the third set after appearing to struggle with a nasal problem.
Earlier at Nottingham, Olympic champion Zheng Qinwen battled back to beat Maria Sakkari 4-6 7-6 (7-1) 6-4.
Queen's finalist Emma Raducanu and Katie Boulter both withdrew from the tournament on Monday.
Jones breaks through after 'hardest moment of career'
