Rafael Nadal brushed aside his strongest challenge at the Australian Open and moved into the fourth round of on Friday without dropping a set.

It took Nadal one hour and 55 minutes to defeat Slovakia's Lukas Lacko, the last qualifier in the draw, 6-2, 6-4, 6-2 and advance to the fourth round for the sixth time.

Unlike the one-sided score turned out to be, Nadal had to fight for his points early in the match. Both players lost their opening service games in a see-saw start to the match, Nadal then had to withstand heavy pressure to hold his second.

But Nadal was quick to settle into his stride, taking advantage of Lacko's uncertain first serve and overpowering the Slovakian with a powerful backhand.

With Lacko's resistance falling to a similar level in the third, Nadal opened up, blasting through the set in 33 minutes to cruise into the fourth round.

Nadal, who is bidding to win his second Australian Open, had to fight against his left knee apart from top seed Novak Djokovic and the third-ranked Roger Federer.

Nadal, who won in the 2009 but has stopped in the final eight due to injuries in the last two years, felt sharp pain in his troublesome right knee while sitting in a chair at his hotel on the weekend.

Medical tests revealed no serious damage, but he has had the knee heavily taped in his three matches since.

On the women's side, third-seeded Victoria Azarenka advanced after she beat Mona Barthel 6-2, 6-4 in a match between champions of two warmup tournaments.

Azarenka only lost eight games at Melbourne Park en route to the Round of 16. The 22-year-old from Belarus will next meet Czech player Iveta Benesova, who beat Russian qualifier Nina Bratchikova 6-1, 6-3.