MELBOURNE, Australia (AP) — Appearing uncomfortable for much of the match, defending champion Novak Djokovic held on to beat David Ferrer 6-4, 7-6 (4), 6-1 and complete a blockbuster semi-final line-up at the Australian Open.

He leads the top four men in tennis into the semis at Melbourne Park — Djokovic against number four Andy Murray, who won his quarter-final match earlier yesterday 6-3, 6-3, 6-1 over Kei Nishikori of Japan.

Today, number two Rafael Nadal plays number three Roger Federer, the first time the two former top-ranked stars have met in a semi-final 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 US 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.

The Nadal-Federer semi-final match-up 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.

On the women’s side, former and reigning Wimbledon winners Maria Sharapova and Petra Kvitova — two of the three players who can take the number one ranking — advanced to the semi-finals.

Sharapova won 6-2, 6-3 on Wednesday against fellow Russian Ekaterina Makarova, who knocked out five-time champion Serena Williams in the previous round. Kvitova reached the semi-finals 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 number one — third-seeded Victoria Azarenka — plays defending champion Kim Clijsters in the other semi-final today.

Sharapova must repeat her 2008 Australian title run if she is to take over the number one spot from Caroline Wozniacki, who lost any chance of maintaining her top ranking when she lost in the quarter-finals 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.