It came on another day paved with nostalgia as siblings Serena and Venus Williams set-up a first women's singles final since Wimbledon in 2009.

Federer, who, at 35, becomes the oldest Grand Slam finallist since Ken Rosewall at the age of 39 at the 1974 US Open, won a tough first set before romping through the second.

Wawrinka battled back to claim the third and fourth to take a spellbinding encounter to a decider.

It was Federer who was able to recover the initiative to win the decider for a 7-5, 6-3, 1-6, 4-6, 6-3 victory.

"I couldn't be happier right now," he said.

"I felt like everything happened so quickly at the end, I had to check the score.

"I never ever in my wildest dreams thought I'd come this far in Australia. 

"It's beautiful, I'm so happy."

Federer, whose last major title was at Wimbledon in 2012, will now face either arch-rival Rafael Nadal of Spain or Bulgarian Grigor Dmitrov in the final on Sunday (January 29).

It will mark his 28th Grand Slam final and 100th Australian Open match.

Nadal and Dmitrov are set to play tomorrow.

The Williams sisters will meet for the ninth time in a Grand Slam final after each surviving semi-final tests today.

Venus, the 13th seed, overcame fellow American Coco Vandeweghe 6-7, 6-2, 6-3 to reach her first major final since 2009.

Second ranked Serena then thrashed Croatia's unseeded Mirjana Lucic-Baroni 6-2, 6-1.

Serena, the 35-year-old, who is one-year younger than her sister, is seeking a record 23rd Grand Slam singles title.