Melbourne, Australia, 25 January 2012 | AAP

Raging title favourite Novak Djokovic says his “intense” battle with Lleyton Hewitt has steeled him for the business end of the Australian Open.

The all-conquering Serb will carry an 18-match grand slam winning streak into his quarter-final on Wednesday with Spanish fifth seed David Ferrer.

His impressive numbers aside, Djokovic was pleased and relieved to have finally endured – and survived – some “ups and downs” to harden him up for greater challenges ahead after cruising through the first week for the loss of just 10 games in nine sets.

“Look, you must expect that you experience some lows, as well, not only highs,” Djokovic said.

“It’s good that you experience these things – bad games, bad movements at this stage of the tournament, prior to the quarter-finals now.”

After leading by two sets and 3-0 in the third, Djokovic dropped his first set of the tournament and had to stave off break points in the fourth before shaking Hewitt off 6-1 6-3 4-6 6-3 in just shy of three hours.

The top seed said the tough workout was just what he needed.

“It’s obviously the first match that I’ve been tested,” Djokovic said.

“It was against the player that I expected to be tested. Lleyton was playing in front of his crowd. Obviously he loves competing against the top guys on the big stage and he proved it again.

“Credit to him as well for being competitive, for not giving up. This is something you can expect from Lleyton, who is very well-known for his fighting spirit.

“But, look, he had the crowd, he had the big support. It got intense.

“Especially the start of the fourth set, we had some great rallies. It’s good to come out from this match as a winner.

“It was a really big challenge for me to see where I stand.”

After piling up 64 wins from his first 66 matches in 2011, the Australian, Wimbledon and US Open champion lost four of his last outings as his phenomenal season took its toll.

But the 24-year-old believes his form, despite his mid-match hiccup against Hewitt, is good.

It will need to be against Ferrer, one of the few players to claim Djokovic’s scalp last year, having defeated the fatigued superstar 6-3 6-1 at the World Tour Finals in London.

Djokovic leads the Spaniard 6-5 overall and 5-2 on hard courts.

“In my eyes, David Ferrer and every player, especially the ones from the top, are great competitors and I have lots of respect towards them,” Djokovic said.

“I think sometimes they’re underrated, especially Ferrer, who has been so consistent. He’s been a top-five player for a long time.

“I cannot underestimate any opponent.”