SAN DIEGO, Calif. -- No.28 Zheng Qinwen advanced to the second round of the San Diego Open after Garbiñe Muguruza was forced to retire down 5-0 in the first set due to GI illness. Zheng will face World No.1 Iga Swiatek in the second round Thursday. 

A finalist at the Toray Pan Pacific Open two weeks ago, Zheng fell in the final round of qualifying to Camila Osorio, 4-6, 6-4, 7-6(3). She gained entry into the main draw on Tuesday as a lucky loser, after Wimbledon champion Elena Rybakina withdrew earlier in the day with an illness. 

"Actually, yesterday I could also sign in as lucky loser but I didn't choose to sign in because I was having an issue with my body," Zheng told reporters in San Diego. She tripped and fell in her final round of qualifying and did not feel well enough to play on Monday.

"Today I was feeling better so I decided with my team to sign in as a lucky loser. I was lucky to get into the draw and I had a good. match today. To get into the next round, it's double lucky." 

Zheng's victory sets up a French Open rematch against Swiatek. The two stars faced off for the first time in Paris this spring, with Zheng taking the first set before losing 6-7(5), 6-0, 6-2 in the Round of 16. It was the only set Swiatek lost during her dominant title run. 

Match report: Swiatek survives Zheng Qinwen to advance to French Open quarterfinals

Zheng's first-set performance left a big impression on Swiatek, who was in the midst of her 37-match win streak at the time. 

"It's hard for me to say how she plays on a hard court because I didn't really watch her matches," Swiatek said in Paris. "I felt on my racquet today that she can play some really heavy topspin, and I feel like if she's going to use it the right way she can really be a great player.

"Honestly, staying in WTA on a top level, it's a mix of many things. So it's hard to say really, but I hope she's gonna stay here, because she can really play great tennis, that, I know."

Zheng struggled physically in the match, but the 20-year-old walked away confident that she was ready to challenge the best in the game.

"She's a good mover, she has a good slide on hard courts," Zheng said. "She has a good forehand and spin. She opens the court very well with the forehand cross.

"It will be a tough match. All the matches she makes, she makes the opponent feel they always have to be there to get the match, she will not give the match easy away. I think the key to play against her is to fight and play until the very end. Just play my game, she will play hers, and then we'll see the fight from each other."