Roger Federer wonder shot sinks Ivo Karlovic

The 16-times grand slam winner admits audacious lob swung momentum of the match in his favour.

Roger Federer in full flow against Ivo Karlovic.

MELBOURNE // Trying to lob a player who stands 6ft 10in is risky at the best of times, let alone on set point, but Roger Federer's gamble against Ivo Karlovic on Friday helped him reach the fourth round of the Australian Open.

Karlovic proved a real handful for the third-seeded Swiss, who struggled to combat the sharp angles the Croat was achieving with his big serve, Federer hanging in and waiting for his chances in the 7-6 7-5 6-3 victory.

Federer's guile and footwork swept him into position to punch returns down the line or back across court which kept him in the match as he took the first set to a tiebreak.

The 16-times grand slam winner looked in trouble when Karlovic had a 6-5 lead and a blooped a volley over the net with Federer scampering to chase it down.

"I didn't know what to do," Federer said of what happened next as he desperately lunged for the ball. "Probably left and right, going to go too slow and he's going to slam it home.

"Let me try the lob, even though that's not what you're supposed to do against him.

"I got sort of the angle right and was able maybe to surprise him, we're that close to each other, so it's hard to kind of react quickly maybe (upwards)."

The tactic worked, the 32-year-old Karlovic mistiming his jump and the ball pinging off the top of his racquet.

"It is like one in, I don't know, a hundred that I'm going to lose that point ... it was really unlucky," Karlovic said.

"I didn't really expect him to do that, but I was there. I just miscalculated how much on (my) jump. It was really unlucky.

"Then if I would have won that, everything would have been different. But that is life, you know. Tennis, that's how it is."

Federer agreed the shot had swung the momentum in his direction.

"It kind of worked, and then I had a great return after that (to set up his own set point). I was almost home. So it was a good turn of events for me then," he added.

"After that, I maybe relaxed a bit. I got a bit of a better read on his serve potentially and just, you know, also knew what I wanted to do also on my own service games.

"It was a big first set, clearly."

Federer, who had overpowered Russian qualifier Alexander Kudryavtsev in the first round then had a walkover in the second round, felt the Karlovic match had been a good workout.

"I think it was important to face throughout the whole three sets just the pressure of facing a guy like Ivo who can serve his way out of trouble, keeps you on your heels the whole time," Federer said.

"I think that was a good thing. Overall I feel good. It's been a good match for me and a good last week."

The 30-year-old is now scheduled to meet the winner of the match between Australian teenager Bernard Tomic and 13th-seeded Ukrainian Alexandr Dolgopolov in the fourth round and Federer said he would be a keen spectator later on Friday.

"I'll follow it as much as I can, because both are quite particular," he said. "I've only played Bernard and Alexandr once each, I think, so I don't know them that well.

"It's going to be a good match to watch. Either player is going to be a challenge for me."