He leads the top four men in tennis into the semis at Melbourne Park — Djokovic against No. 4 Andy Murray, who won his quarter-final match earlier Wednesday 6-3, 6-3, 6-1 over Kei Nishikori of Japan.
On Thursday, No. 2 Rafael Nadal plays No. 3 Roger Federer, the first time the two former top-ranked stars have met in a semifinal since the 2005 French Open.
It marks only the third time that the top four seeds have advanced to the semis at the Australian Open — previously it was in 1988 and 2005. It was also the 14th time at all Grand Slams since the Open Era began in 1968, but it has happened in three of the last four — after the U.S. Open and French Open last year.
Djokovic rubbed the back of his upper left leg on several occasions, looked on the verge of being physically sick in the second set and buried his head in towels several times during breaks. Late in the third set, a tired-looking Djokovic sat down on a linesman's chair during a line-call video challenge by Ferrer.
"I was lucky to get out of the second set, it was a big mental advantage to get two sets up," Djokovic said.
An hour after the match, Djokovic further played down the possibility of any injuries, saying: "I don't have any physical issues."
"I feel very fit and I feel mentally, as well, very fresh," he told his post-match news conference. "It's just today I found it very difficult after a long time to breathe because I felt the whole day my nose was closed a little bit. I just wasn't able to get enough oxygen."
Ferrer said he couldn't be sure if Djokovic was healthy — or not.
"You have to ask to him," Ferrer said, "he ran perfect all the match. Nothing special."
The Nadal-Federer semifinal matchup has been rarely possible because the pair held the top two spots for most of the time between 2005 and 2010, meaning they could only meet in the finals after being placed in opposite sides of the draw.
Djokovic said he'd be watching the Nadal and Federer match like any tennis fan.
"I will enjoy it from my couch, they're two out of four or five of the greatest players to play this game, they've been so dominant," Djokovic said. "Every time they play it's a treat. I'm going to have a nice dinner at home and watch them."
Murray, for his part, is also surprised to be not facing Nadal in the semifinals.
"It has been amazing, I pretty much drew to be in Nadal's half ... almost every Slam," Murray said. "I can't remember the last time I wasn't in his half of the draw. It's been a long time."
In men's doubles action, Toronto's Daniel Nestor and Belarusian partner Max Mirnyi reached the semifinals, defeating Santiago Gonzalez of Mexico and German Christopher Kas 6-1, 6-7 (4-7), 6-2.
Nestor, 39, has played in four Australian Open doubles finals and won the title with Mark Knowles of the Bahamas a decade ago.
"We came her to win the event," Nestor said. "We've gone this far but the matches are only going to get tougher.
"That's why we had the short off-season and came early to Brisbane. Hopefully we can win, it's been a long time for me here."
On the women's side, former and reigning Wimbledon winners Maria Sharapova and Petra Kvitova — two of the three players who can take the No. 1 ranking — advanced to the semifinals.
Sharapova won 6-2, 6-3 on Wednesday over fellow Russian Ekaterina Makarova, who knocked out five-time champion Serena Williams in the previous round. Kvitova reached the semifinals at Melbourne Park for the first time with a 6-4, 6-4 win over unseeded Italian Sara Errani.
The other player who can reach No. 1 — third-seeded Victoria Azarenka — plays defending champion Kim Clijsters in the other semifinal Thursday.
Sharapova must repeat her 2008 Australian title run if she is to take over the No. 1 spot from Caroline Wozniacki, who lost any chance of maintaining her top ranking when she lost in the quarterfinals to Clijsters. Kvitova only has to match or better Azarenka to take the top spot.
Sharapova has dropped one set and lost 21 games in five matches.
"It's been a long road back to this stage," said Sharapova, who spent 10 months off the court with a shoulder injury that required surgery.
Sharapova held the No. 1 ranking for seven weeks each in 2005 and 2007 and three weeks in mid-2008.
"I've been fortunate enough to be in that position before," Sharapova said. "I think the girls that are trying to get that position haven't been in that position before. It's a little bit different because I feel like I've experienced both things in my career: winning Grand Slams and being No. 1 in the world. You can't compare the two."
In junior play, Vancouver's Filip Peliwo defeated Czech Marek Routa 4-6, 6-3, 6-3 in the third round. But Peliwo and Serbian partner Pedja Krstin lost 6-4, 6-7 (6), 10-3 tiebreak to Australians Andrew Harris and Nick Kyrgios in the doubles quarter-finals.
Second-seeded Eugenie Bouchard of Montreal beat American Christina Makarova 7-5, 7-5 in third-round girls' play.
Bouchard and Carol Zhao of Richmond Jill, Ont., were beaten 6-4, 6-2 by Ilka Csoregi of Romania and Elizaveta Kulichkova of Russia in their quarter-final.