Battling Serena edges past Zheng
Serena Williams set a new Wimbledon women's record with 23 aces as the sixth seed was given a "gut check" by China's Jie Zheng.
Williams previously held a 5-0 win-loss record over Zheng, but the Chinese produced some excellent tennis to make the American look ordinary at times on the Centre Court where she has previously won four Wimbledon titles.
Zheng often matched Williams for skill and athleticism, but the American's powerful serving enabled her to record a 6-7 (7/5) 6-2 9-7 win.
Williams, who beat Zheng in the 2008 Wimbledon semi-finals, was impressed with the performance of her 28-year-old opponent.
"She played unbelievably well," said Williams, who faces Sara Errani's conqueror Yaroslava Shvedova in round four.
"I kept fighting in that third set. If I was going to go out I wanted to go out fighting.
"It was good to go through. I needed a tough match like that."