Zheng Qinwen has described her slow return to form as a painful rebirth that left her questioning herself and led to “uncomfortable conversations” with her parents and coaches.After months of struggling on the tour, the Chinese star has returned to form at the US Open, and produced a second thrilling win in a matter of days on Monday in New York, battling back from 5-0 down to beat Iga Swiatek in straight sets to reach the quarter-finals.The former world No 4 has been in such poor form for the past year, that she had dropped to 125th in the rankings and needed to come through qualifying just to reach the main draw.Now the 23-year-old is the first qualifier to reach the last eight since Emma Raducanu came through from nowhere to win the tournament in 2021.“I think the process of rebuilding myself is a very painful one, especially when I constantly have to face failure: OK, it’s not just one loss, the next match, OK, you lose again, and you have to ask yourself why all the effort you put in seems useless. And then comes the next match,” Zheng said in an interview with Chinese state broadcaster CCTV.“I think, for me, these past three or four months have been basically the worst period of results in my career. Even when I talk to myself, [I] find it unbelievable: why did it turn out like this? Is it simply because I was injured for so long without touching a tennis racquet, and my muscle memory was so slow to return?”