MELBOURNE--Defending champion Novak Djokovic and the player he beat in last year's final, Andy Murray, advanced in contrasting styles at the Australian Open on Tuesday.

World number one Djokovic ripped through Italian journeyman Paolo Lorenzi for the loss of just two games, while fourth seed Murray needed over three hours and four sets to douse young American Ryan Harrison.

Djokovic oozed confidence in disposing of the 109-ranked Lorenzi 6-2, 6-0, 6-0 in only 1hr 32min in high temperatures on Rod Laver Arena and will play Colombia's 56th-ranked Santiago Giraldo in the next round.

But Murray was kept on court for 3hr 12min on Hisense Arena before ousting the 77th-ranked Harrison, 4-6, 6-3, 6-4, 6-2.

Djokovic is brimming with confidence after his sensational 2011 when he claimed three of the four grand slams and seized the top ranking from Rafael Nadal last July.

Only four men on five occasions have won three or more consecutive grand slams in the open era—Rod Laver, Pete Sampras, Nadal and Roger Federer twice.

"I feel much more complete as a player and as a person as well," Djokovic said. "Mentally I've gained a lot of experience playing at the top level in the last couple of years.

Novak Djokovic will play Colombia's 56th-ranked Santiago Giraldo in the next round.

Last year's Australian Open triumph was the first of seven straight tournament wins in a 41-match streak that was finally ended by Roger Federer in the semi-finals of the French Open.

Murray, bidding to become Britain's first male major winner since Fred Perry in 1936, is looking to go one better than his shattering defeats to Federer and Djokovic in the past two Australian Open finals.

He has enlisted tennis great Ivan Lendl as his new coach and is unbeaten in six matches this year after winning the Brisbane International earlier this month.

The Scot recovered from his early setback to gain control over Harrison and only lost nine games in the closing three sets to wrap up victory and a second-round meeting with Frenchman Edouard Roger-Vasselin.