Top seed Caroline Wozniacki continued her quest for a first slam with a comfortable 6-2 6-2 victory over Romania's Monica Niculescu in the third round of the Australian Open.

The 21-year-old world number one was broken by the 31st seed when she was serving for the match at 5-1 but the hard work had already been done under overcast skies on Hisense Arena.

She wasted no time in breaking back immediately to clinch the victory with a rasping backhand winner after 76 minutes and reach the fourth round without dropping a set.

The Dane, who has to reach at least the quarter-finals in Melbourne to reamain at the top of the rankings, was eager to focus afterwards on on-court matters rather than dwell too long on how her progress would affect her standing.

"To be honest I just play," 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. If I do that I know I can play on a very high level.

"If you win tournaments, then the ranking will be there automatically."

Victoria Azarenka, one of three players who could usurp Wozniacki from the top spot - Petra Kvitova and Maria Sharapova are the others, kept up the pressure with a 6-2 6-4 victory over Mona Barthel.

Although the result was never in doubt, the match ended on a controversial note when Azarenka issued a verbal volley to a linesperson after squandering four match points.

The third-seeded Belarusian revealed afterwards the outburst was a ploy to wind herself up to get over the line.

"I had to get a little bit angry to get my emotions going to finish the match, because I had a few chances and I didn't convert them," she said.

"Sometimes you just have to push yourself a little bit to get you going again.

"I am a very emotional player."

Next up for Azarenka is Czech Iveta Benesova, who thrashed Russian qualifier Nina Bratchikova 6-1 6-3, while Wozniacki meets Jelena Jankovic, a 6-2 6-0 victor over American Christine McHale.

Champion Kim Clijsters made up for her Brisbane International semi-final disappointment against Daniela Hantuchova earlier this month with a polished 6-3 6-2 victory over the Slovak.

The 28-year-old Clijsters quit with a hip injury while a set ahead against Hantuchova in Brisbane but said prior to the Australian Open began that it had healed completely and would not hamper the defence of her title.

Clijsters had spent less than two hours in total on court in the first two rounds at Melbourne Park and continued her ruthlessly efficient progress through the tournament against the 20th seed, converting five of 11 break point opportunities to seal a comfortable win.

Eighth seed Agnieszka Radwanska progressed with a 6-2 6-2 win against Galina Voskoboeva, as did 22nd seed Julia Goerges who beat Romina Oprandi 3-6 6-3 6-1.