London - Four-time champion Serena Williams needed an ace performance to hold off a gutsy challenge from China's Zheng Jie at Wimbledon on Saturday, with "Marathon Man" actor Dustin Hoffman cheering her on.
The US sixth seed showed her grit to come back from a set down to win 6-7 (7/5), 6-2, 9-7 on Centre Court to propel her into the fourth round.
The Chinese 25th seed provided Williams with a serious examination over nearly two and a half hours, but the American showed she has lost none of her gritty determination as she finally made the breakthrough.
Williams fired 23 aces - a Wimbledon women's singles record - to make it into the last 16.
A wealth of British sporting stars were in the royal box, along with US golf hero Jack Nicklaus and former Wimbledon champions Martina Navratilova and Boris Becker.
But Williams had plenty of star quality in her own box, with Hoffman joining her family on Centre Court.
"I knew that he would be there. Major fan of his. Who isn't a fan of Dustin Hoffman? I was honoured to have him in my box. He's invited anytime," Williams said.
"I haven't had a chance to talk to him yet, but I probably will.
"I don't know him, I just think he's a great actor. That's more than enough. I mean, come on, 'The Graduate'! He's an award winning actor and seems like a great person."
Zheng hadn't been past the Wimbledon second round since becoming the first wildcard to reach the semi-finals at the All England Club four years ago.
The 28-year-old, who was beaten by Williams on that occasion, was making only her second appearance in the last 32 of a Grand Slam since 2010.
"It's a long match, and also it's a tough match because she has a big serve. It's very difficult against her on the grass court," she told AFP.
"But I think I played well. Just a few points. I had some chances, like the final set, fourth game, I'm 2-1 up, and I have the three break points, but I missed.
"And in the final set, seven-all, my service game, the serve is was not so good.
"But I think it's a great match for me, also."
Williams faces Yaroslava Shvedova of Kazakhstan for a place in the quarter-finals after the wildcard knocked out 10th seed Sara Errani of Italy, the French Open runner-up, 6-0, 6-4, taking every point in the first set.
There were no breaks of serve in the first set, which saw precious few points conceded on serve as both players refused to give ground.
Zheng produced a comical serve in the sixth game when, with the sun in her eyes, she served into her own half of the court, the ball bouncing over the net like a ping-pong serve.
Zheng took a 5-2 lead in the tie-break and though Williams levelled, she made two errors that handed the Chinese the set.
Williams dominated the second set, breaking in the fifth game then stepping up a gear to take the next three games to love.
The Chinese had three break points in the fourth game of a pulsating final set but some Williams aces and Zheng errors took it to 2-2.
Williams broke at 7-7 and though Zheng then held off two match points, she could not survive the deuce, leaving Williams looking somewhat relieved.
Wimbledon women's singles last 16 line-up (x denotes seeding):
Maria Sharapova (RUS x1) v Sabine Lisicki (GER x15)
Kim Clijsters (BEL) v Angelique Kerber (GER x8)
Agnieszka Radwanska (POL x3) v Camila Giorgi (ITA)
Maria Kirilenko (RUS x17) v Peng Shuai (CHN x30)
Serena Williams (USA x6) v Yaroslava Shvedova (KAZ)
Francesca Schiavone (ITA x24) v Petra Kvitova (CZE x4)
Tamira Paszek (AUT) v Roberta Vinci (ITA x21)
Ana Ivanovic (SRB x14) v Victoria Azarenka (BLR x2)