Serena Williams survived by far the biggest first-week test of her Wimbledon campaign as she came from a set down to see off the gutsy challenge of 25th seed Jie Zheng.
Williams previously held a 5-0 win-loss record over Zheng, but the Chinese produced some excellent tennis today 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 - she registered a remarkable 23 aces - 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."
Williams, whose sister Venus was knocked out in the first round by Elena Vesnina, wasted little time or energy in blasting past Melinda Czink on Centre two days ago.
But Zheng made the American aware that she would provide a much sterner test.
Zheng had her opponent racing to all corners of the court in the opening exchanges and earned three break points in the third game after Williams slipped on the baseline.
Williams saved the first with an ace and after two errors from the Chinese, the four-time champion powered down two more aces, the second a 119mph rocket, to hold.
Williams was put off by the breeze in the first-set tie-break as she aborted her ball toss on the first point. The American then lost focus to send a simple backhand long.
Williams let out a typically forceful scream of "Come on!" as she broke back to level at 5-5 in the breaker, but Zheng was unmoved and soon clinched the set when forcing the American to hit a backhand wide.
Any hopes Williams had of an immediate break in the second set were dashed when Zheng held to love, but the American inflicted damage in the fifth game when her opponent ploughed the ball into the net at 30-40.
Zheng's fight seemed to have evaporated as she was broken to love in the seventh and Williams served out to level the match.
The deciding set was tense but peppered with Williams aces.
Zheng showed nerves of steel to hold to love and lead 5-4.
Both players refused to back down and the set moved to 7-7, at which stage Williams earned her first break point of the set.
Zheng survived that but gave Williams another opportunity moments later, and this time the chance was taken as the underdog fired long after a powerful Williams forehand.
Despite an early double fault when serving at 8-7, Williams engineered two match points at 40-15.
Zheng showed she still had fight in her by returning two sharp backhands to force deuce.
But when it arrived the sixth seed did not squander a third match point, she leapt up with clenched fists, clearly delighted to have avoided a shock defeat.