As a furious David Nalbandian vowed to fight his 'Watergate' fine, Djokovic did his best to cheer up struggling Mahut on his 30th birthday by happily playing to the crowd as he dispatched the Frenchman 6-0, 6-1, 6-1.

Mahut, compromised by a left knee injury, maintained his good humour and he shrugged and smiled broadly to fans as he finally won his first game at the start of the second set. He was later given a birthday cake by reporters.

“Credit to Nicolas. Obviously, he had some strapping around his knee and I felt sorry for him,” said defending champion and top seeded Djokovic, who remains on course for a semi-final with Andy Murray.

“Evidently he was not moving well, he was not able to perform his best, but he didn't want to retire and he wanted to stay all the way so I wish him happy birthday.”

Mahut, who lost the longest match in tennis history at Wimbledon 2010, was not the only injury casualty on day six as Russia's Maria Kirilenko became the second women's retirement in quick succession.

Just hours after Anabel Medina Garrigues agonisingly rolled her ankle against Li Na late on Friday, Kirilenko lasted until just game two of the second set against Petra Kvitova before retiring with a thigh problem.

Wimbledon champion Kvitova took another step towards seizing the world number one ranking from Caroline Wozniacki, setting up a round four match with Serbia's Ana Ivanovic, who won in straight sets against Vania King.

Maria Sharapova, who lifted the women's trophy four years ago, won 6-1, 6-2 against Angelique Kerber.

But misfiring former world number two Vera Zvonareva departed in tears after she was shocked by 56th-ranked fellow Russian Ekaterina Makarova. China's Zheng Jie also upset France's number one, Marion Bartoli, 6-3, 6-3.

Former finalist Jo-Wilfried Tsonga blazed into the fourth round for the loss of just six games against Portugal's Frederico Gil -- all without a coach.

“You can also improve your game by yourself. I've improved a lot,” said the Frenchman. “I'm here because maybe I had a coach, but now I feel like I have to follow my opinion maybe a bit more.”

Fellow Frenchman Richard Gasquet also reached the fourth round and Spain's David Ferrer came through in three sets against Juan Ignacio Chela.

And there were more fireworks from Nalbandian as he hit out against his hefty $ 8,000 fine for splashing water at an official following his stormy exit in the second round.

“During anti-doping control, I was washing my hands and the doctor incredibly accused to me of throwing water at him,” he tweeted.

“Two injustices -- one inside and another one outside the court. I am going to appeal the sanction.”

In tempestuous scenes, Nalbandian had argued vociferously on court when he was refused a Hawk-Eye challenge at the climax of his five-setter with John Isner.