Novak Djokovic has made the stunning confession that he once feared he may wind up as a one-slam wonder.

Now the world No.1 is potentially days away from landing a record fifth Australian Open crown and joining Andre Agassi, Ivan Lendl, Jimmy Connors, Ken Rosewall and Fred Perry as an eight-times grand slam champion.

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After rolling through his first three matches without dropping a set, Djokovic enters the second week of the Open an odds-on favourite to surpass Agassi and Roger Federer as the only man in almost half a century of professional tennis to win five titles in Australia.

Yet the 27-year-old has revealed how he was riddled with self doubts before gaining “wings” after leading Serbia to a historic first-ever Davis Cup trophy in 2010.

Djokovic reacts after beating Andy Murray. Photo: Getty

“I remember in the first couple of years in my professional career I won my first grand slam at the Australian Open in 2008 and after that I struggled for several years,” Djokovic told AAP.

“I had a lot of self doubts, didn’t know if I could really make it.

“I lost most of the matches to Federer and (Rafael) Nadal in the major events.

“But I made that breakthrough at the end of 2010 and had my best year of tennis in my life in 2011, 40 wins in a row, which gave me wings and the confidence for where I am now.”

And where he is now is on the threshold of joining some of the legends of the game on the all-time grand slam leaderboard, with Federer (17), Nadal (14), Pete Sampras (14), Roy Emerson (12), Rod Laver (11), Bjorn Borg (11) and Bill Tilden (10) the only other players ahead of Djokovic.

The top seed is oozing confidence after passing his first serious test this campaign with flying colours.

With an imperious serving display, Djokovic dispatched 31st seed and former semi-finalist Fernando Verdasco 7-6 (10-8) 6-3 6-4 to book an Australia Day date with unseeded Gilles Muller.

Verdasco said Djokovic was almost unplayable on Rod Laver Arena as he landed 75 per cent of his first serves.

“Returning his serve was so tough,” the Spaniard said.

“He was serving so close to the lines and in every direction.

“It was difficult to read it and to keep the ball in play.”

The dominant display dispelled any lingering doubts about Djokovic’s fitness after he struggled with the flu and a stomach bug on the eve of the season’s opening major.

Having been unable to practise properly pre-event, Djokovic said nothing beats court time.

“It’s a great confidence booster if you are on the court, if you have great memories and you won the tournament four times,” he said.

“I’m always trying to have that in the back of my mind, the great performances I had over the years. I try to use that in my advantage.”

Victory over Muller on Monday would thrust Djokovic into a clash with either eighth seed Milos Raonic or 12th seed Feliciano Lopez.