Melbourne – Novak Djokovic remained on track to defend his Australian Open title with another dominant win to reach the fourth round as South African Kevin Anderson scored an upset Friday.

Two-time defending champion Djokovic was untroubled to serve his way into the last 16 with a straight sets win over never-say-die Czech Radek Stepanek.

Out on Hisense Court, Anderson, just outside the seedings, eliminated 22nd seed Fernando Verdasco in five sets to earn a crack at either Czech fifth seed Tomas Berdych or Austrian Jurgen Melzer in the fourth round.

World No 1 Djokovic, bidding for his fourth Australian crown, didn't allow Stepanek a look in as he completed a 6-4, 6-3, 7-5 victory in an entertaining 2hr 22min on Rod Laver Arena.

Djokovic has yet to drop serve in three dominating wins at this year's Open and has only had five break points against him in 43 service games.

The top seed will next face either American 20th seed Sam Querrey or Swiss 15th seed Stanislas Wawrinka in the round of 16 on Sunday.

“Radek loves the big stage. You saw how much fun he had. I also had a lot of fun playing. It was a very entertaining match,” he said.

“It was three close sets. I felt that I had much more chances on his serve than he had on my serve.”

Stepanek, the hero of the Czech Republic's Davis Cup final triumph over Spain last November, kept charging in at Djokovic and ventured to the net 67 times to try to seize the initiative.

“I have respect for him because he's a fighter, he's a competitor, and somebody that is one of the rare players who comes to the net nowadays and mixes up his style of the game,” said Djokovic, whose 37 winners to 19 unforced efforts ratio underlined his form.

Anderson, who lost to Australian Bernard Tomic in last weekend's Sydney International final, is bidding to emulate fellow South African Wayne Ferreira, who reached the semi-finals here in 2003.

He needed 3hr 46min before subduing the big-hitting Verdasco 4-6, 6-3, 4-6, 7-6 (7/4), 6-2 for his first win in three encounters with the Spaniard.

Elsewhere, Japan's 16th seed Kei Nishikori kept on the winning trail for a 7-6 (7/3), 6-2, 6-3 victory over Russian Evgeny Donskoy in 2hr 6min.

Nishikori, who reached the quarter-finals of the Australian Open last year in the best Grand Slam performance by a Japanese man, will take on the winner of the David Ferrer-Marcos Baghdatis match scheduled later Friday.

Serbian eighth seed Janko Tipsarevic was taken to his second consecutive five-setter before overcoming Frenchman Julien Benneteau and will next face Spanish 10th seed Nicolas Almagro in the last 16.

Almagro ended Polish 24th seed Jerzy Janowicz's tournament, winning in three hard-fought sets. – Sapa-AFP