Fourth seed Coco Gauff has resisted a fierce challenge from Marta Kostyuk to book a spot in the Australian Open semi-finals for the first time.

The reigning US Open champion extended her grand slam-winning streak to a dozen matches with a rollercoaster 7-6 (8-6) 6-7 (3-7) 6-2 victory in Tuesday’s first women’s quarter-final at Melbourne Park.

But Gauff had to scrap for more than three hours in scorching heat as 21-year-old Kostyuk, fighting for a higher force, overcame painful blisters to threaten a huge boilover.

“I’m happy, really proud of the fight that I showed today,” the American said.

“Marta is a tough opponent. Every time we play, it’s a tough match and I really fought and left it all on the court today.”

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Six years after making the last 32 in Melbourne at just 15, Kostyuk has used this Open campaign to shine the light on Russia’s war on her Ukrainian homeland.

She questioned why Russian and Belarusian players were even allowed to compete at the tournament and showed a similar resolve against Gauff.

But the underdog eventually yielded, wilting in on-court temperatures exceeding 30 degrees Celsius as Gauff progressed to a semi-final on Thursday against either second-seeded defending champion Aryna Sabalenka or Czech ninth seed Barbora Krejcikova.

Kostyuk had made a blazing start, breaking Gauff twice in the first six games to charge to a 5-1 lead in the opening set.

But, serving for the set, she coughed up consecutive double faults to gift Gauff a foothold into the match.

Kostyuk had a set point serving again at 5-3 but was broken once more, then for a third time in a row, to fall behind 6-5.

Just as Gauff looked like snatching the set, the fourth seed faltered with a double-fault of her own on break point.

Kostyuk needed a medical timeout before the tiebreaker to have her bandaged left foot treated.

She battled on bravely and conjured a second set point, only to dump two forehands into the net as Gauff eventually claimed the opener after 78 minutes.

Sensing her opportunities were slipping away, Kostyuk threw her racquet in disgust after blowing further break-point chances in the third game of the second set.

The 21-year-old looked then almost resigned to defeat after dropping serve for a fifth time to trail 4-2, then 5-3.

Almost inevitably, though, the epic quarter-final took another twist as Kostyuk broke back in the ninth game and levelled the match on a second tiebreaker.

But giving up such a huge first-set lead ultimately took its toll physically as Gauff raced to a 5-0 lead, then finally claimed victory after three hours, eight minutes to leave Kostyuk’s equally inspired compatriot Dayana Yastremska to keep the Ukraine flag flying in Melbourne.

Yastremska plays unseeded Czech teenager Linda Noskova in the quarter-finals on Wednesday, with Chinese world No.15 Zheng Qinwen up against Russian Anna Kalinskaya in the remaining women’s last-eight encounter.

-AAP