Former world number one Garbine Muguruza was thrashed 6-0 in her first set at the Australian Open and could barely train because of a viral illness. Now she's in the semi-finals for the first time.

The 26-year-old Spaniard plays Simona Halep in the last four in Melbourne on Thursday, just two victories away from her third Grand Slam title. It is all a far cry from the first round when Muguruza -- unseeded at a Grand Slam for the first time since 2014 -- folded 0-6 in the first set to American qualifier Shelby Rogers.

"I came not feeling great. I wasn't really thinking, how far will I go?" Muguruza said after defeating Russian 30th seed Anastasia Pavlyuchenkova in Wednesday's quarter-finals. "I had enough already thinking, how will I go practise today?"

Muguruza, now 32 in the world after a slump last year, roared back 6-1, 6-0 in the next two sets to beat Rogers. She has not looked back and is enjoying good health once more.

"I took every day at a time. Like that, each day I was gaining a better feeling instead of getting frustrated thinking in the future," she said. "It's definitely been from low to high, not starting at my best, then each day recovering."