Federer masterclass on dramatic day

Roger Federer handed out a masterclass to Australian teen Bernard Tomic as he reached the quarter-finals on a day of tears and drama at the Australian Open Sunday.

While Federer was at his mesmerising best and Rafael Nadal also went through, China's Li Na left in floods of tears after she fell victim to an astonishing comeback by hobbling women's champion Kim Clijsters.

And ear-splitting boos greeted Tomas Berdych's win over Nicolas Almagro as the Czech player refused to shake hands at the end of their stormy match. Nineteen-year-old Tomic, the great hope of Australian tennis, could only shake his head in disbelief as Federer dug into his bag of tricks and unleashed his full repertoire of unreachable drops and a balletic backhand smash.

"I thought I played a really good match. I knew I had to, anything else and I wouldn't have got the job done," said the Swiss world number three, who stays on course for a grandstand semi-final with Nadal.

"The score would suggest otherwise. If you hadn't seen the match you would think straight sets, no problem, but I had to work extremely hard and Bernard showed why he is going to be a great player in the future."

Nadal, seeking his 11th major victory and his second Open crown, beat fellow Spanish left-hander Feliciano Lopez 6-4, 6-4, 6-2 to reach the quarter-finals without dropping a set.

The powerful second seed kept Lopez at bay with serving accuracy of 80 percent and he piled on the pressure with nearly error-free tennis to stay unbeaten on hardcourts against his Davis Cup team-mate.

Nadal will play Berdych in the quarter-finals while Federer has a testing match-up with Juan Martin del Potro, his conqueror in the 2009 US Open final, who beat Philipp Kohlschreiber of Germany.

Belgium's Clijsters looked on the verge of quitting when she rolled her left ankle in the first set, and despite gritting her teeth and playing on she looked down and out facing four match points in the second-set tiebreak.

But the despairing Li saw Clijsters save all four, culminating in a brave drop-and-lob combination -- and the Belgian took the set as the flustered Chinese netted, and then went long.

It proved a dramatic tipping point as errors flowed from the racquet of French Open champion Li, who was broken immediately in the third set and could not claw her way back despite pleas from her coach and husband Jiang Shan.

Li recovered to break as Clijsters served for the match but the Belgian made no mistake on her next service game, clinching a famous win on her second match point when her Chinese opponent netted.

"It has to be," said a disbelieving Clijsters, when asked if it was her greatest comeback. "I can't believe I won. I knew before the match it was going to be a tough match... but I didn't expect this."

The result was a carbon-copy of last year's gripping final when Li, as the first Chinese player in a grand slam singles title match, took the first set but then fell to pieces as Clijsters came roaring back.

Li gave a testy press conference which was hastily broken up when the distraught Chinese player dissolved in tears and fled from the room.

Elsewhere Berdych was booed mercilessly by the crowd for refusing to shake Almagro's hand, claiming the Spanish player aimed a ball at his face.

Meanwhile Victoria Azarenka defeated Czech Iveta Benesova 6-2, 6-2 to set up a quarter-final with her close friend Agnieszka Radwanska, who brushed aside Germany's Julia Goerges 6-1, 6-1.

Clijsters will play world number one Caroline Wozniacki, who sent Serbia's Jelena Jankovic out in straight sets.