Coco Gauff, US Open & ASB Classic winner, into the Australian ...

Coco Gauff of the U.S. plays a forehand return to Marta Kostyuk. Photo / AP Photo

Coco Gauff kept alive her hopes of back-to-back Grand Slam singles titles after beating Marta Kostyuk 7-6 (6), 6-7 (3), 6-2 in an error-strewn quarterfinal match at the Australian Open on Tuesday.

The U.S. Open champion had 51 unforced errors, nine double faults and just 17 winners but battled past Kostyuk in three hours, eight minutes.

The 19-year-old American has now won 12 straight matches in Grand Slams.

“I’m really proud of the fight I showed today,” said Gauff, who plays either defending champion Aryna Sabalenka or ninth-ranked Barbora Krejcikova in the semis.

“Marta’s a tough player, we always have close matches,” Gauff added. “I really fought and left it all out on the court today. In the second set, I had an opportunity but I think I got passive. When I came out in the third I really tried to be a bit more aggressive.”

Having lost just 15 games on her way to the quarters, Gauff was vulnerable early on against Kostyuk, the Ukrainian who was appearing in her first Grand Slam quarterfinal.