Madison Keys faces the biggest test of her resurgence when she meets Ash Barty in the Australian Open semi-finals on Thursday, as the American aims to end the top seed's bid to delight home fans by winning an elusive title.

Keys, who reached the last-four in 2015, will play in her first Grand Slam semi-final in four years having emerged from the "dark pit of despair" she had fallen into due to the pressure she put on herself to perform at the highest level.

"I know I'm going to feel nervous... excited. I know all of those feelings are going to be there," Keys said of her previous semi-final appearances at majors. "But it's also a completely different situation, time and person.

"I think you take the experience that you have from those moments and you try to apply it, but you also know that it's going to be a completely different challenge."

Keys can expect a tough time against a ruthless Barty, who is chasing a third Grand Slam title to add to her French Open and Wimbledon crowns, and also become the first local player since Chris O'Neil in 1978 to triumph at Melbourne Park..

Danielle Collins takes on former Roland Garros champion Iga Swiatek in the other semi-final, looking to secure a first win over the seventh seed and break into the top 10 of the world rankings.(Reuters)