MELBOURNE (AFP) -- Novak Djokovic says he motivates himself with "trash talk" after returning to form to sweep past 30th seed Tomas Martin Etcheverry and into the fourth round in his 100th match at the Australian Open on Friday, Jan. 19.

The 10-time champion dropped sets in each of his first two matches but was never in trouble in his third-round contest against the Argentine, cruising to a 6-3, 6-3, 7-6 (7/2) win.

The Serbian world number one has been under the weather in Melbourne, searching for form and struggling with a virus which he said was in its final stages.

Despite the comfortable nature of the win on Rod Laver Arena, Djokovic occasionally looked frustrated with himself, exchanging gestures with his coaching team.

"It's not always a positive pep talk," he said. "There's a lot of trash talk happening inside of my head.

"I guess it's part of the game, it's part of who I am. I mean, I'm quite certain that everyone goes through their crisis moments, particularly in the matches where they don't feel their best and they have doubts."

He added: "I'm trying to fight the demons that I have, as anybody else, on the court."

Djokovic did not face a single break point in the match, which brought up a century of appearances at his most successful major -- he now trails only Roger Federer (117) and Serena Williams (105).

The top seed, chasing a historic 25th Grand Slam title, which would break his tie with Margaret Court, broke in the sixth game of the first set for a 4-2 lead and he closed out the set.

The 36-year-old was quickly back on the attack in the second set, breaking for a 2-1 lead against his 24-year-old opponent, who ousted Andy Murray and Gael Monfils from the tournament, and he broke again to take the set.

Etcheverry dug deep in the third set and took it to a tie-break but there was a sense of inevitability about the outcome, with Djokovic firing an ace to seal victory in just under two-and-a-half hours.

Despite the ease of his progress the Serb, who will face French 20th seed Adrian Mannarino in the last 16, said he had yet to hit his top level.

"I played better than I did in the first two rounds, so that's a positive change, I guess. Starting to feel better game-wise and physically, as well. It's positive signs.

"I still haven't been playing at my best."