Melbourne:An invincible Roger Federer moved a step closer to a record-equalling 14th Grand Slam title on Tuesday as Novak Djokovic's defence of his Australian Open crown ended in misery.
The Swiss star was in awesome form as he thrashed young Argentine pretender Juan Martin del Potro 6-3, 6-0, 6-0 to set up a semi-final with Andy Roddick, who went through after Djokovic withdrew from their match with cramp.
Meanwhile, Russia's Dinara Safina overcame dogged resistance from Jelena Dokic to win 6-4, 4-6, 6-4 and end the Australian's comeback tournament after years of depression sparked by the antics of her infamous father Damir.
The third seed will now meet seventh-seeded compatriot Vera Zvonareva for a place in the final after the Russian coolly disposed of France's Marion Bartoli 6-3, 6-0. World number two Federer is now in his 19th consecutive Grand Slam semi-final.
"I played great tonight, I didn't expect a result like this," said the Swiss, who is chasing his fourth Australian Open title in his quest to equal Pete Sampras's all-time Grand Slam record.
"For me, it is a fabulous effort, I'm delighted. When all of a sudden it clicks, it's a nice thing."
Earlier, Serbia's Djokovic was trailing 7-6 (7/3), 4-6, 2-6, 1-2 in furnace-like conditions to Roddick when he signalled that he could not continue.
In an Open that has produced plenty of surprises, he became the fourth player to pull out of the quarter-finals either injured or ill, following Zheng Jie, Victoria Azarenka and Gael Monfils.
Djokovic blamed his retirement on cramps and the heat, with the mercury reaching 35 C (95 F).
There appears to be little respite in store with forecasters warning the city is this week heading for its worst heatwave in 100 years, with 40 C plus temperatures predicted every day.
"People could see that I was struggling with movement, the main reason is cramping and soreness in the whole body," said Djokovic, adding that organisers needed to look again at their heat policy.
"That's something we have to discuss in the future. Of course, it's concerning a lot of players," he said.
"As a tournament or as a tennis fan, you don't want to see a player retiring. You didn't pay for a ticket to come to see somebody retiring the match."
The seventh seeded Roddick, looking for another Grand Slam title to go with his US Open crown in 2003, was playing high-class tennis when Djokovic withdrew and may well have progressed regardless.
But he said the victory was hollow. "I feel for Novak because he worked so hard to win the title and for him not to get a fair chance to defend it, it's too bad," Roddick said.
"But I was pretty happy with everything. I just kind of stayed the course. I felt good."