Roger Federer could scarcely comprehend his run to the Australian Open final, after a tumultuous semi-final win over Stan Wawrinka put grand slam number 18 within his grasp.

Federer beat his compatriot 7-5 6-3 1-6 4-6 6-3 to snap a run of losing semi-finals and book his first Melbourne showpiece appearance since 2010 - becoming the oldest major men's finalist in over 40 years in the process.

Rafael Nadal could be a dream opponent in the final - the Spaniard plays Grigor Dimitrov in Friday's second semi - and chatter of two men with 31 grand-slam titles between them has buzzed across Melbourne Park.

Federer himself could hardly hide his desire to take on Nadal for the ninth time in a grand-slam final.

"It's real now," he told two-time Melbourne champion Jim Courier on court. 

"I can actually talking about playing a final for the first time. I've been dodging that bullet for the last couple of days. 

"I'll leave it all out here in Australia and if I can't walk for another five months, that's OK.

"Rafa is the biggest challenge. This court allows me to be offensive. I'm probably his number one fan. 

"We've had some epic battles over the years. It would be unreal to play here. 

"I don't think either of us thought we were going to be here potentially playing in the final because I went to open his academy in Mallorca with him a few months back and I told him 'I wish we could do a charity match or something'.

"But I was on one leg and he had the wrist injury and we were playing some mini tennis with some juniors and we were like 'it's the best we can do right now'. 

"A few months later, we are maybe going to be in the finals. It's a very special tournament for us already."

A stunning comeback from two sets down by Wawrinka was stymied when he crucially served a double fault in the decider to put Federer on the path to victory.

"I did feel he gave a bit of a cheap break," Federer said. "I didn't really deserve it at that moment. But I served it out. 

"Everything happened so quickly at the end. I had to check the scoreboard. 

"I never, ever in my wildest dreams thought I would come this far in Australia. I've got a couple of days off. I'm so happy."