By Ian Ransom

MELBOURNE (Reuters) - Roger Federer and Rafa Nadal starred for the old establishment in a daytime double-feature at the Australian Open Friday before two rising talents threatened to steal the show with a thrilling tussle under the bright lights of Rod Laver Arena.

Federer felled towering Croat Ivo Karlovic to follow Nadal into the last 16 and stay on collision course for a mouth-watering semi-final against the Spaniard who eased past Slovakian Lukas Lacko.

The real drama came later, however, when young home favorite Bernard Tomic edged a five-set classic against Ukraine's Alexandr Dolgopolov to justify his prime-time billing.

After three hours and 49 minutes of tension-charged action, the rangy 19-year-old with nerves of steel emerged with a 4-6 7-6 7-6 2-6 6-3 victory and the prospect of a fourth round battle with Federer.

"Tonight was a really good match and a match that I need to win," the Germany-born Tomic said in a courtside interview after knocking out the 13th seed. "I think the crowd made me win so thankyou for coming out and supporting me guys."

On a day of almost total dominance for the seeds, 2009 champion Nadal raised the curtain at Rod Laver Arena with a 6-2 6-4 6-2 drubbing of Lacko.

Arriving in Melbourne with questions about his form, fitness and motivation, Nadal has not lost a set so far and never appeared in danger against his 119th-ranked opponent under overcast skies on center court.

Only a low-flying bird swooping across the court stalled the Mallorcan's charge momentarily as Nadal set up a fourth-round clash with fellow Spaniard Feliciano Lopez.

Lopez outlasted towering marathon-man John Isner in a five-set duel, the American's second in a row at the tournament, to leave the U.S. without a single man in the last 16 of the Australian Open for the first time since 1973.

"That's not a good effort from the Americans this tournament," Isner said.

"I knew going in today I was the last one left and I wanted to keep on going, but just didn't happen."

Third seed Federer achieved the seemingly impossible when he managed to salvage a set point with a winning lob over the 2.08m beanpole Karlovic who had briefly threatened the Swiss with a barrage of booming serves.

With Karlovic leading 6-5 in the first set tiebreak, Federer's lob from just in front of the net pinged off the top of Karlovic's racket allowing the Swiss maestro to save the set and roll on to emphatic 7-6 7-5 6-3 victory.

"After that (lob), I maybe relaxed a bit. I got a bit of a better read on his serve potentially and just also knew what I wanted to do on my own service games," said Federer, chasing his 17th grand slam crown after a barren 2011 in the majors.

With Rod Laver Arena hogged by the men's contenders, Caroline Wozniacki's battle for credibility as the world number one continued on the second show court against 31st seed Monica Niculescu.

Dane Wozniacki needs at least one more win in Melbourne to have a chance of emerging from the year's first grand slam at the top of the women's rankings, a position she has held for 67 of the last 68 weeks despite not winning a grand slam title.

With three other players having a chance to snatch the top ranking after the dust settles at Melbourne Park, the Dane signaled she would not give up the prize without a fight as she steamrolled the Romanian 6-2 6-2 in 76 minutes.

"To be honest, I've proven myself for the last two years. I've finished number one twice in a row," the blonde 21-year-old said, defending her ranking yet again.

"For me, the most important thing is to keep improving. If I do that, I know I can play on a very high level."

Wozniacki will play Serb Jelena Jankovic, a former world number one whose own grand slam ambitions are yet to be fulfilled.

Defending champion Kim Clijsters marched on with a 6-3 6-2 romp over Slovakian Daniela Hantuchova.

The Belgian, soaking up her valedictory year on tour, faces a re-match of last year's final with French Open champion Li Na in the next round, after the Chinese advanced when her opponent Anabel Medina Garrigues retired in tears with injury.

Garrigues's right ankle rolled underneath her while trailing 2-0 in the first set and the Spaniard had to be helped off. After lengthy treatment she returned to play another game before pulling out.

Victoria Azarenka, one of the three plotting a coup against Wozniacki, maintained the heat on the Dane with a comfortable 6-2 6-4 victory over Germany's Mona Barthel.

Former U.S. Open champion Juan Martin del Potro, the only man to have broken the grand slam oligopoly shared by Federer, Nadal and world number one Novak Djokovic in recent years, moved

quietly into the fourth round with a straight-sets win over Taiwan's Lu Yen-Hsun.

Czech Tomas Berdych, the 2010 Wimbledon finalist, was another flying under the radar. The seventh seed ground to a 7-6 7-6 6-1 win over 2.03m (6-foot-8) South African Kevin Anderson to complete a disappointing day for the games' giants.

(Editing by Martyn Herman)