Watson was in total control against Zhang – who reached the final of last week’s Viking Open Nottingham – breaking her opponent twice and smashing seven aces as she cruised to a 5-1 lead. She had a chance to wrap up the set, playing a sublime drop shot winner to set up a sole set point, but Zhang rallied to hold serve and deny her opponent.

But after stopping for the second time in the match to get medical help for her heavily-strapped knee, the 32-year-old was forced to throw in the towel and hand Watson a spot in the quarter-finals.

“I could tell from the first point she wasn’t at her best,” Watson said. “She had such a great week last week so I’m not too surprised given all the great tennis she’s been playing.

“Even though she was hurting I was very happy with how I was striking the ball today, so hopefully I can bring that into my next match.”

Next up for Watson is Croatia’s Donna Vekic, the number three seed, who overcame Italy’s Camila Giorgi in a thrilling three-set contest with a 2-6, 6-3, 6-4 win.

After losing the first set 6-2 Vekic bounced back to claim the second 6-3 and after sailing to a 5-1 lead in the third the World No. 54 let five match points slide by.

Eventually Vekic, who has won twice on the WTA Tour, kept her cool to wrap up the match – watched on by her dog, a miniature poodle cross called Mali.

“Camilla played great, she’s so fast,” Vekic said. “You know it is coming but you’re still surprised every time you face her. I’m really happy I was able to serve it out.

“After I lost those match points I just tried to stay aggressive and stay calm and focus on my serve. “Mali means ‘little’ in Croatian and it’s great to have him here this week.”