Indeed, it was not until the latter stages that Djokovic finally displayed some of the form which saw him dominate the rest and win three grand slam crowns in 2011.

Fifth seed Ferrer, as always, was a game opponent but lacked the weapons to trouble Djokovic, who ran out a 6-4 7-6 (7/4) 6-1 winner to advance to a clash with Andy Murray in a repeat of last year's final he won comfortably.

When quizzed about a possible fitness issue afterwards, Djokovic was giving nothing away.

"You have to hang in there, David is a great competitor and he always makes you hit every shot," he said. "I wasn't feeling very fresh.

"It was a great match, we played for almost three hours - I think the first 30 minutes was just for the first two games.

"I was lucky to get out of the second set and that was a big mental advantage to go two sets up."

It was a result which further emphasised the gulf between the top four players and the rest as a seemingly struggling Djokovic beat the fifth best player in the world convincingly.

Although evident at the end, there seemed little between them in the early stages as Ferrer matched Djokovic stroke for stroke in some punishing baseline exchanges.

And it took a moment of brilliance from the top seed to break for 3-2 with a stunning forehand.

Despite being pushed when serving for the set he got the job done and then broke in the opening game of the second.

He may have been in command on the scoreboard but Djokovic's demeanour was not that of a man enjoying his evening's work.

Ferrer, perhaps sensing all was not well with his opponent, broke back for 2-2 and the momentum swung further in his favour when Djokovic pulled up sharply in the next game clutching his hamstring.

The top seed battled on though and even broke for a 6-5 lead only for Ferrer to hit straight back. The tie-break would prove the pivotal moment of the match.

Ferrer led 4-2 but Djokovic showed great resolve to battle back and claim the next five points and finish the set with his first fist pump of the night.

The third set was a cruise as Djokovic finally freed his shoulders and Ferrer wilted.

Earlier, Murray brushed aside the challenge of Kei Nishikori to ease into his third successive semi-final in Melbourne.

The world number four was rarely troubled by the Japanese, winning 6-3 6-3 6-1 in two hours and 12 minutes, as he maintained his smooth progress through the draw.

Murray will have better days on serve - he got just 44% of first serves into play - but, that aside, there was little room for improvement in a good all-round performance.

"It was a good match, a lot of fun points, most of them he was winning so I was trying to keep them as short as possible," said Murray.

"But I need to serve better, I didn't serve particularly well but the returning was good so that was a positive.

"My game has been getting better each match and I am moving better and I am going to be fresh going into the weekend."

Nishikori, the first player from Japan to reach the last eight here in 80 years, showed glimpses of his potential but, like Murray's previous opponent Mikhail Kukushkin, seemed fatigued by his efforts in previous rounds.

The 22-year-old from Shimane had spent four hours more on court than Murray in reaching this stage and it showed.