Zeng, 19, looked on track for a big upset as she claimed the first goal in a tiebreak before Swiatek took control to win 6-7 (5), 6-0, 6-2 for her 32nd straight win.
Cheng said she wasn’t in any pain during the opening set, but it took her medical time to trail 3-0 in the second, massaging her back on court before going into the locker room and back with her right thigh strapped.
“Yes, my legs were also tough,” Cheng, the world number 74, told reporters. “It was easy compared to the stomach… I can’t play tennis, my stomach was very painful.”
“It’s just girls’ stuff, you know. The first day is always really hard and after that I have to work out and I’m always so sore the first day. And I can’t go against my nature.
“I wish I was a man in court, but I can’t at that moment… I really wish I was (a man) (so) I shouldn’t have to suffer from this.”
Cheng, who made her grand slam debut at this year’s Australian Open, said she did her best to compete but was happy that she advanced into week two.
She added, “If I don’t talk about it today, I’m happy with my performance (in) this round. Playing against the number one in the world, I felt I really enjoyed (this) on the court.”
“If I didn’t have (pain) in my stomach, I think I could have fun more, like running better and hitting harder, to do more on the court. It’s a pity that I couldn’t do what I wanted to do today.”
“I just want (so that) the next time I play against her, I’m (in good shape).