Andy Murray reached the second round of the Shenzhen Open after China's Zhang Zhizhen retired.
Former world number one Murray led 6-3 6-7 (3-7) 4-2 when Zhizhen, a wildcard at the event in China, ended the match.
The Briton, now ranked 311th as he continues his comeback from hip surgery, saved eight break points as he was given a stern test by the world number 340.
He will face Belgian top seed David Goffin in the next round.
Murray, a wildcard in Shenzhen, is appearing in his penultimate event of the year after deciding to end his season early.