British teenager Mika Stojsavljevic was denied a first WTA win after an agonising 6-4 6-7 (7-9) 7-6 (8-6) defeat by Japan's Moyuka Uchijima in the first round of the Pan Pacific Open.
The 15-year-old, the reigning US Open girls' champion, held a 3-2 lead against Uchijima in the first set before she was broken three times in a row to lose the opener.
Stojsavljevic, who was playing in her first main-draw match, saved two match points in the second set and went on to win the tie-break 9-7 to level the match.
She took that momentum into the deciding set, breaking Uchijima, ranked 57th in the world, to take a 5-2 lead.
But the world number 633 missed the opportunity to serve out the match, allowing 23-year-old Uchijima to level at 5-5.
In the tie-break, Stojsavljevic saved two more match points but Uchijima recovered to see out the win.
Uchijima will face top seed Zheng Qinwen in the second round in Tokyo.
Elsewhere, British number one Katie Boulter is through to the last 16 after easing to a 6-1 6-4 win against Australia's Priscilla Hon.
The 28-year-old broke the Australian three times in the first set, converting 100% of her break points.
It was similarly straightforward for Boulter in the second set as she broke Hon, ranked 184 places below her, twice.
The world number 33 will play Japan's Kyoka Okamura next.