Doubts setting in for Novak Djokovic?

MELBOURNE, Australia -- Novak Djokovic did exactly what he wanted against Lleyton Hewitt in the early stages of Monday's hotly anticipated clash at the Australian Open.

The world No. 1 took the crowd on Rod Laver Arena out of the match by getting off to a sizzling start. But then a strange thing happened; very strange -- and slightly worrying for Djokovic's supporters.

Up two sets and 3-0 in the third, the wheels came off. Djokovic was stretched to four sets and even had to fend off a break point in the infancy of the fourth when the score was tied.

He finally put the banged-up Hewitt away 6-1, 6-3, 4-6, 6-3 to reach the quarterfinals.

"It was so unusual, and because of that, alarm bells," said Mark Woodforde, half of the legendary "Woodies" doubles team and now an analyst with Australian television. "Djokovic was just playing at such a high level. Then to kind of bottom out. Hewitt's dogged determination got him back in there, but I don't know whether it was exceptional play by him or Djokovic becoming really frail."

The statistics suggest it was the latter.

Djokovic's serve and forehand, in particular, tailed off.

In the first two sets, he made a combined five forehand unforced errors. The number rose to 14 in the last two. His first-serve percentage fell in the middle of the third, and overall Djokovic was broken four times.

"Certainly noticed the first-serve percentage disappeared, and the forehand," Woodforde said. "He was able to fight off any opponent with those two specific shots in 2011. I think in the past, when he was forming as a tennis player, there was so much pressure on his serve, and hence that kind of shaky technique. And when it was really falling apart, his forehand looked like the obvious weakness. I was surprised it showed up last night. If I was one of his opponents, I would think that there's some glimmer of hope."

Djokovic explained the reasons for the blip, and he indeed knew it was a blip, after the match.

"Between that part, 3-0, third set and the beginning of the fourth, I wasn't moving at all," he said. "I was pretty passive in the rallies, giving him the opportunity to come in. But look, you must expect that you experience some lows, not only highs."

Djokovic's next opponent, fifth seed David Ferrer, is similar to Hewitt: He hustles for every ball and is a fine returner. But at this juncture of their careers, he's better than Hewitt. Mind you, Ferrer won't be the overwhelming crowd favorite Wednesday, as "Rusty" was.

"He's been a top-five player for a long time," Djokovic said.

Ferrer won't be overawed confronting the man who won three of the four Grand Slams last year, especially if he watched the end of Monday night's affair.

He topped Djokovic at the year-end championships in London in December, and even if the Serb was fatigued, Ferrer will take confidence from the 6-3, 6-1 victory indoors.

That result allowed Ferrer, a semifinalist in Melbourne last year, to edge closer in their head to heads. He trails 6-5.

Ferrer was his usual humble self when looking ahead to the match.

"He is the world No. 1 and is better than me at everything," Ferrer told reporters in Spanish. "I'll try to play at a good pace, play my game. I'm not going to do anything different because I'm playing Djokovic. What happens is that I'll have to play aggressively and play the important points better than in a normal match."

Woodforde said Djokovic will have more to answer because of his lapse versus Hewitt. But added, "If he played like he did at the start, I think he'll handle Ferrer."

It's not a massive "if," but Djokovic's mid-match swoon against Hewitt raised some doubts.

Prediction: Djokovic in four.

Andy Murray (4) versus Kei Nishikori (24)

Nishikori became the first Japanese man to reach a Grand Slam quarterfinal since his mentor, Shuzo Matsuoka, in 1995 and the first to reach a quarterfinal at the Australian Open in the Open era. As such, the buzz back home has been ample.

And when asked what the past 24 hours have been like, his agent at IMG, Olivier van Lindonk, replied in an email: "Busy!! From a business point of view [we've] been very active in the past years setting up the platform to make him one of the biggest earners in tennis. Every time he breaks records, this platform keeps growing. Obviously all the people that have helped him over the years have reached out."

Including Matsuoka.

In Murray, Nishikori -- who last season surpassed Matsuoka as Japan's highest-ranked men's player ever -- battles a similarly well-sponsored athlete.

At this stage, however, Murray is the better player, well rested and eased past Nishikori in Shanghai in October.

Prediction: Murray in three.

Maria Sharapova (4) versus Ekaterina Makarova

Monday turned out to be a great day for Sharapova. Not only did she rally to beat heavy serving German Sabine Lisicki, but the flat-hitting Makarova, ranked 56th, took care of Serena Williams.

It means Sharapova gets her fellow Russian in the quarterfinals instead of Williams, who crushed the fourth seed in their last meeting in California in the summer.

"Either way, it doesn't matter," Sharapova said. "For [Makarova] to come in and win in straight sets and to play at that level means she's obviously on a pretty big high note right now confidence-wise. And that's always dangerous."

But how many times have we seen a player fall flat following a major upset?

Prediction: Sharapova in two.

Petra Kvitova (2) versus Sara Errani

Errani is a diminutive Italian who chases every ball, which can be highly frustrating for opponents. And like Makarova she'll be full of confidence, given she's advanced to her first Grand Slam quarterfinal. Call it a surprise that it happened away from Roland Garros.

Errani, No. 48, didn't need to beat anyone in the top 30 to progress to the last eight, although she routed an in-form Zheng Jie in the fourth round.

Kvitova, the towering Wimbledon champion, mostly impressed in a straight-set win over Ana Ivanovic.

Errani will need Kvitova to have a major off day to go any further.

Prediction: Kvitova in two.

London-based Ravi Ubha covers soccer and tennis for ESPN.com. You can follow him on Twitter.