U.S. Open champion Coco Gauff came through a huge test at the hands of Ukrainian world number 37 Marta Kostyuk 7-6(6) 6-7(3) 6-2 to reach the semifinals of the Australian Open for the first time on Tuesday.

The fourth-seeded American will rarely play as badly and still progress but prevailed after more than three hours on a blistering hot Rod Laver Arena to fulfill her coach Brad Gilbert's famous maxim by "Winning Ugly."

"I'm really proud of the fight I showed today, Marta's a tough opponent, every time we play it's a tough match," she said.