Britain's Cameron Norrie was left to rue missed opportunities as he was beaten by rising teenage star Learner Tien in the Shanghai Masters third round.
World number 33 Norrie fell 7-6 (7-4) 6-3 to the American on another hot and humid evening.
Norrie came back from a break down in the first set and served for the opener before Tien regrouped to take the eventual tie-break.
Norrie then missed three break points early in the second set before losing his serve in the next game, and later missed another two chances to break back.