SHANGHAI, China: World number seven Ons Jabeur defied a bad knee on Thursday to finally defeat Italian Lucia Bronzetti 6-3, 7-6 (7/5) and reach the quarter-finals of the Zhengzhou Open. Playing with her right knee taped, the Tunisian three-time Grand Slam finalist failed to serve out the victory on three occasions and needed five match points to move past the 63rd-ranked Italian in just under two hours. A champion in Ningbo two weeks ago, Jabeur will next face eighth seed Daria Kasatkina, who beat home player Bai Zhuoxuan 6-2, 6-4. “It was a tough finish obviously, she’s a great player, such a fighter,” said the 29-year-old Jabeur. “So, I’m glad that I got to finish in two (sets). It would have been a different story if it was three sets. We will learn a lot from this match. “I tried to do my best, it’s the end of the season and it’s very, very tough with the knee. Today it wasn’t 100 percent.” A seesaw opening set saw a combined five breaks of serve but it was Jabeur who carved out a 5-2 gap and the Tunisian took a one-set lead after 45 minutes. The fourth seed earned a double-break lead in the second set and looked on track for a smooth victory when she served for the match at 5-2. But Bronzetti had other ideas and snatched the next three games, breaking Jabeur twice to level the frame for five-all, saving a match point along the way. Jabeur stopped the bleeding as she used her signature drop shot to maximum effect to break Bronzetti and put herself in position to serve for the win for a third time. Still the North African could not close as Bronzetti saved three more match points and broke serve on a Jabeur double fault to take the set into a tiebreak. Jabeur finally closed out the 74-minute second set, and the contest, on her fifth match point. Kasatkina also had to overcome a second-set fightback from her opponent and needed four match points before she completed a 90-minute victory over 117th-ranked Bai. The 26-year-old Russian has lost her last five matches to Jabeur. “Ons is an amazing player, she’s creative on the court and you never know what to expect from her,” said Kasatkina. Germany’s Laura Siegemund upset 11th seed and recent Beijing runner-up Liudmila Samsonova 3-6, 6-2, 6-1 to book a quarter-final against Italian Jasmine Paolini.