Hopefully got the bad match out of the way: Gauff

'Today was frustrating because I knew how I needed to play. I just couldn't execute.'

Coco Gauff eked out a victory to reach her first Australian Open semi-final on Tuesday and while the victory was more graft than glamour the US Open champion was just fine with that.

The three-hour, eight-minute battle against Ukrainian world number 37 Marta Kostyuk took nearly as long as three of her previous four matches at Melbourne Park combined, with Gauff eventually prevailing 7-6(6), 6-7(3), 6-2.

Her normally reliable serves and returns let her down, but she managed to claw her way back from a 5-1 deficit in the first set, one point at a time.

"I think today was definitely a C game, so didn't play my best tennis - but really proud that I was able to get through today's match," Gauff told reporters. "Hopefully got the bad match out of the way and I can play even better."

The World number four, playing a Grand Slam for the last time as a teenager, lived out her coach Brad Gilbert's strategy, captured in his tennis manual "Winning Ugly".

"I bought a copy but I didn't read it," said Gauff, who is looking to become the first woman in three years to win the US Open and Australian Open back-to-back.

"But, you know, I feel like I got the real version so I don't need a book. But maybe it could help."

The strategy paid off, making up for shots that she said she is normally able to make but was "missing by a lot" against Kostyuk.

"Today was frustrating because I knew how I needed to play," she added. "I just couldn't execute. Eventually I was able to find it, which is what I'm proud of. But, yeah, problem-solving is tennis."

Undaunted by the scorching heat on Rod Laver Arena, which she said was not as hot as back home in Florida, Gauff was forced to rely on her mental game strength to make up for her below-par shot-making.

"I think that's gotten me through a lot of matches, and I feel like mentally I'm one of the strongest out there, and I try my best to reset after each point," she said.

Next up she will face either world number two Aryna Sabalenka, whom she beat to clinch the U.S. Open last year, or ninth seed Barbora Krejcikova.

"The goal is to stay here as long as possible and keep going upwards," said Gauff. "I mean, I'm not at the top but I'm up there."