British number two Heather Watson is into the last eight of the Birmingham Classic after China's Zhang Shuai retired while trailing 5-2 in the first set of their match.
Watson had lost three of their previous four matches but hit seven aces in three service games and broke twice before Zhang stepped off the court.
The world number 36 was apparently hindered by an injury to her left leg.
"From the first game, she wasn't moving quite right," said Watson.
"I knew her leg was taped and I knew that was bothering her.
"I just made sure I focused really hard on my serves and returns and I actually hit them better than I have for a long time.
"It's tough but you just have to pretend she is 100%."
Watson, 29, will play Donna Vekic in the quarter-finals after the Croat beat Italy's Camila Giorgi 2-6 6-3 6-4 earlier on Wednesday.
Former French Open champion Jelena Ostapenko and Russian fourth seed Daria Kasatkina are among the possible semi-final opponents on the same side of the draw.
At the WTA event in Berlin, the top three seeds fell in the last 16, with world number four Aryna Sabalenka losing to American Madison Keys, Elina Svitolina beaten by Russia's Ekaterina Alexandrova and Bianca Andreescu knocked out by France's Alize Cornet.
That means the draw has opened up kindly for Swiss Belinda Bencic, who advanced to the quarter-finals with a 6-3 6-4 win over Petra Martic.
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