Novak Djokovic last night admitted to having breathing difficulties during his win over David Ferrer at the Australian Open but insisted it would not hamper his chances against Andy Murray in Friday's semi-final.

Serbia's Novak Djokovic after winning yesterday's quarter-final clash
against Spain's David Ferrer. Pic/AFP

Djokovic cut an unhappy figure for much of his match against the Spaniard despite winning 6-4, 7-6 (7/4), 6-1 to keep his title defence on track.

And the World No 1, who has previously undergone sinus surgery, revealed afterwards he had been struggling for air.

Scottish ace Andy Murray celebrates his win over Kei Nishikori in
yesterday's quarter-final. Pic/Getty Images

"I found it very difficult after a long time to breath because I felt the whole day my nose was closed a little bit," he said.

"I just wasn't able to get enough oxygen. I needed more time which I didn't have but in these conditions, at this stage of the tournament, when you're playing someone like David, your physical strength and endurance come into question.

"But I am not too concerned about that at all.

"I'm really fit and I have no concerns of recovering for the next match. It's just a matter of breathing better through the nose."

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

The World No 4 was rarely troubled by the Japanese, winning 6-3 6-3 6-1 in two hours and 12 minutes.