AFP - Roger Federer edged a five-set thriller against his fellow Swiss and close friend Stan Wawrinka at the Australian Open on Thursday to become the oldest Grand Slam finalist in 43 years.

The 17-time Grand Slam champion saw off the world No. 4 7-5, 6-3, 1-6, 4-6, 6-3 in three hours and five minutes and will face either Rafael Nadal or Grigor Dimitrov in Sunday's final.

It will be 35-year-old Federer's sixth Australian final and 28th Grand Slam decider in total, and caps a marvellous comeback after the second half of last season was ruined by a knee injury.

The four-time Australian Open champion becomes the oldest man to reach a Grand Slam final since Australia's Ken Rosewall (39 years 310 days) at the 1974 US Open.

In an enthralling contest, Federer won the opening two sets before Wawrinka clawed back to take the semi-final into a fifth, only for Federer to prevail with a service break in the sixth game.

"Yes, it is real now. I can talk about playing in finals for the first time," Federer said on court.

"I have been dodging that bullet for the last few days now, talking about the next round and the next round but this is the last one.

"So I will leave it all out here in Australia and (even) if I cannot walk for another five months, I will give it all I have."