By Peter Rutherford
MELBOURNE (Reuters) - World number one Novak Djokovic survived an energy-sapping streetfight with David Ferrer and Andy Murray cut Kei Nishikori down to size to reach the Australian Open semi-finals on Wednesday.
Defending champion Djokovic appeared to tweak a hamstring early in the second set as he lunged along the baseline but ground out a 6-4 7-6 6-1 win in two hours, 44 minutes.
Briton Murray had a far less taxing time against Japanese Nishikori, who was walking tall after a shock win over world number six Jo-Wilfried Tsonga in the fourth round.
Murray dominated Nishikori despite struggling on serve, pounding out a 6-3 6-3 6-1 win to set up a semi-final clash with Djokovic.
Another giant-killer, Ekaterina Makarova, failed to build on her stunning upset of Serena Williams and lost 6-2 6-3 to Maria Sharapova, while world number two Petra Kvitova made heavy weather of beating unseeded Italian Sara Errani.
Serb Djokovic has been in majestic form since his Australian Open win kickstarted a stellar 2011 season but it was heart and lungs that got him past Ferrer.
The 24-year-old was bent double, gasping for breath early in the first set as the terrier-like Spaniard dragged him to the four corners of the court in a succession of lung-bursting rallies.
Ferrer doggedly chased down everything thrown at him but was powerless to stop Djokovic's charge to victory as the Serbian found his range with blistering backhands and mixed in some deft dropshots to keep the fifth seed guessing.
"David makes you run, makes you play an extra shot, makes you earn your points," Djokovic said.
"In these conditions, at this stage of the tournament when you're playing somebody like David, somebody that has great shots from both sides from the baseline, makes you always play over five to 10 shots in the rally, your physical strength and endurance comes into question."
Murray's coach Ivan Lendl was on hand to check out the Scot's semi-final opponent and will have been rubbing his hands with glee watching Djokovic being pushed to the limit.
Murray was never in any danger of succumbing to another seismic shock at Melbourne Park against Nishikori, who had ousted Frenchman Tsonga to become the first Japanese man through to the last eight in Melbourne for 80 years.
Cheered on by kimono-clad fans, 24th seed Nishikori did not hang around long enough to be a pain in Murray's neck and the Japanese bowed out with barely a whimper.
"I had a sore neck today when I woke up and I wasn't feeling all my serve. I don't know if it had anything to do with that," the 24-year-old Briton told reporters.
"It's good to see that I've been playing my best tennis at the slams because that's something the last couple years I wanted to make sure I was doing. That wasn't always the case."
Russian Sharapova probably expected a tougher time against compatriot Makarova, who had knocked out five-times champion Williams.
The world number 56 had beaten Williams with venomous backhands and dogged determination but was let down by an insipid serve against Sharapova.
While the Melbourne Park crowd have given fellow primal screamer Victoria Azarenka a hard time throughout the tournament they were more forgiving of the Sharapova shrieks.
Sharapova, who won the last of her three slams at Melbourne Park in 2008, shrugged off the debate about her "grunting" and said she had no plans to tone it down.
"I've been the same over the course of my career. No one important enough has told me to change or do something different," she added.
Sharapova will play Kvitova for a place in the final after the Czech bounced Italian surprise package Errani out of the quarter-finals 6-4 6-4 in the day's opening match.
The diminutive Errani would not have looked out of place in a ball-kids' uniform but measured up well against six-footer Kvitova, refusing to buckle under her brutal backhands.
Kvitova, who beat Sharapova in last year's Wimbledon final, failed to find her rhythm but dug deep for the win.
"At the beginning I was a little nervous because I knew everybody expected it to be an easy match," the 21-year-old told reporters.
"Of course you have a little pressure on your back because you have a grand slam and everybody is expecting that you win all your matches when you play. Bit it's not really easy."
Kvitova, Azarenka and Sharapova are vying to take over the world number one ranking from Caroline Wozniacki, who was knocked out by Kim Clijsters on Tuesday.
(Editing by Ed Osmond)