2016 Australian Open: Nishikori, Sharapova and Williams move into quarterfinals; Djokovic made to sweat

Kei Nishikori, Maria Sharapova and Serena Williams have become the first tennis players to enter the last eight of the Australian Open.

Nishikori roughed out an entertaining 6-4, 6-2, 6-4 win over 2008 edition finalist Jo-Wilfried Tsonga here on Sunday. It's the fifth consecutive year that Nishikori, Asia's highest-ranked player, has made the second week of the year's first Grand Slam, reports Xinhua.

No matter how hard Tsonga tried, the explosive Frenchman could not hit his way past the brick wall-like defence of the Japanese.

Obviously frustrated, pro-Tsonga fans at the Hisense Arena lifted the 30-year-old out of a hole as he faced the prospect of going down a double break in the third set. But, eventually, Tsonga ran out of chances to pull himself back into the game as Nishikori closed out the match in a tick over two hours.

It was more of a slog across on Rod Laver Arena for World No.5 Maria Sharapova. Despite putting together a 7-5, 7-5 victory, the Russian spent more than two hours on court in her fourth round encounter against 12th seed Belinda Bencic.

Sharapova to face Serena Williams

Sharapova was forced to go for a break to gain the ascendency over her younger opponent, hitting an astounding 21 aces and 58 winners. But the 28-year-old's incredible stat-line was tempered by seven double faults and 46 unforced errors.

The 2008 Australian Open champion will now face nemesis Serena Williams in a replay of last year's final after the World No.1 American beat another Russian, Margarita Gasparyan 6-2, 6-1 in the fourth round.

Sharapova, with an 2-18 record against the 21-time Grand Slam champion, has not beaten Williams since 2004.

"It was a great final last year against each other. I came quite close in that second set, but not close enough. I look forward to playing the best in the world and that's what she's proven the last year and many years, and it will be a great match," said Sharapova.

Djokovic earns a hard-fought win

Defending champion Novak Djokovic was stretched to 5 sets by Gilles Simon of France, eventually defeating the Frenchman 6-3 6-7 6-4 4-6 6-3 in a cracking 5-setter.

In his post-match press conference, Djokovic said he was pleased to win the match despite producing one of his worst on-court performances in recent years.

“Unfortunately you have days like this. It’s actually good to win when you play that bad,” Djokovic said.

“In terms of the level I’ve played, it’s a match to forget for me.”

When asked if he had ever hit 100 unforced errors in a match before, the five-time Australian Open winner said he had “never been close”.

“But there’s a first time for everything,” he added.

Djokovic admitted he will need to step up his game on Tuesday, when he faces seventh seed Kei Nishikori, who dismantled world No. 10 Jo-Wilfried Tsonga in straight sets earlier on Sunday.