US Open champion Coco Gauff gave herself only a ‘C’ rating for an error-strewn performance that put her into a first Australian Open semi-final Tuesday, but said she hoped it was a one-off.

The American world number four needed three hours and eight minutes to wear down Ukraine’s unseeded Marta Kostyuk in stifling conditions on Rod Laver Arena 7-6 (8/6), 6-7 (3/7), 6-2.