Caroline Wozniacki & Victora Azarenka win at Australian Open

Caroline Wozniacki
Wozniacki is still searching for her maiden Grand Slam title

World number one Caroline Wozniacki stepped up her Australian Open campaign with a commanding victory over Romanian Monica Niculescu to reach the last 16.

An aggressive Wozniacki saw off the 31st seed 6-2 6-2 to set up a meeting with 13th seed Jelena Jankovic, who beat American Christina McHale 6-2 6-0.

They are joined in the fourth round by third seed Victoria Azarenka, a 6-2 6-4 winner against Mona Barthel of Germany.

Defending champion Kim Clijsters beat Daniela Hantuchova 6-3 6-2.

Wozniacki also negotiated her first two matches in straight sets, but she played with greater authority and variety against Niculescu.

The Dane broke serve in games two and seven of a 36-minute opening set and raced into a 5-1 lead in the second.

Niculescu used her unusual sliced forehand to prevent her opponent serving out the match, but Wozniacki hit straight back to seal victory.

Wozniacki needs to reach at least the quarter-finals to have a chance of retaining top spot in the world rankings.

She said: "I want to try to do my best here and whatever happens, happens.

"I have proven myself for the last two years. I have finished number one twice in a row, and for me the most important thing is to keep on improving."

The next challenge for Azarenka comes in the form of unseeded Czech Iveta Benesova, a 6-1 6-3 winner against Nina Bratchikova.

"I'm playing pretty good," said the Belarusian, who needed four match points to get past Barthel in 88 minutes.

"At the end I was not brave enough to finish the match but I'm glad I managed to in the end - I had to kick myself to finally finish it."

Azarenka destroyed Heather Watson and Casey Dellacqua in rounds one and two, and it seemed a repeat was likely against Barthel.

She took the first set off her German opponent in 31 minutes with two breaks of serve and only three unforced errors.

Barthel showed more grit in the second and after being broken to love in game five, she had break-back points in games eight and 10.

But Azarenka held firm on both occasions to come through, although not without controversy.

On her third match point the 22-year-old felt a Barthel return landed wide, but she had already used all of her Hawk Eye challenges.

She berated both the line judge and umpire before the final point and again once she had served out the match, drawing boos from the crowd on Hisense Arena.

Clijsters made up for her Brisbane International semi-final disappointment against Hantuchova with a polished victory.

The 28-year-old converted five of 11 break points to seal the win and next faces a potential repeat of last year's final against Li Na if the Chinese beats Anabel Medina Garrigues.

Elsewhere, eighth seed Agnieszka Radwanska overcame Galina Voskoboeva of Kazakhstan 6-2 6-2 with a brilliant display.

The Pole goes on to face 22nd seed Julia Goerges of Germany, who came from a set down to beat Italy's Romina Oprandi 3-6 6-3 6-1.