Nadal, Federer advance to Round IV of Aus Open

As John Isner completed the worst ever US men's showing in the open era.u00a0Injury-hit World No 11 Juan Martin del Potro equalled his best Grand Slam performance since winning the 2009 US Open, and Australian teen Bernard Tomic won a rollercoaster five-setter against Ukraine's Alexandr Dolgopolov.

With the 6ft 10ins (208 cm) Karlovic hammering serves from on high and constantly coming forward, blocking the court with his outsized frame, Federer faced an awkward task.u00a0But at set point down in the first set tie-break and scrambling to a drop shot, he did not flinch and gamely aimed a vertical lob over the Croatian beanpole, who could only parry it into his own court.

Federer, deftly combating the sport's fastest serve with his unerring backhand, took his first set point, then conjured the match's first break to take the second set before clinching it 7-6 (8/6), 7-5, 6-3.u00a0"I knew it could come down to a few (points) here and there and obviously you need a bit of luck," he smiled. "I definitely got a bit fortunate and I started to play better as the match went on."

Earlier, Nadal bludgeoned his way into the fourth round with a straight-sets win over Slovakia's Lukas Lacko ufffd but he denied he was having it easy at the year's opening major.

After a hard-fought opening against Lacko, the 2009 champion raced away with it 6-2, 6-4, 6-2.u00a0"Nothing is easy. Everything is difficult. Every match you have your problems," Nadal said:u00a0

"First set was 6-2, but I had to fight for it. It was a tough one. But I played solid all the match, so that's why I won," he added.