'Insane' Gauff powers into Auckland semi-finals

Coco Gauff continued the ruthless defence of her Auckland Classic title on Friday with a 6-1, 6-1 trouncing of Varvara Gracheva to set up a semi-final against fellow American Emma Navarro.

With rain clouds gathering, Gauff was in the mood for a swift victory over her French opponent and achieved it in 52 minutes in another ominous display ahead of the Australian Open.

The world number three and US Open champion clinched the title in Auckland last year without dropping a set and is on track to repeat that feat.

The 19-year-old was particularly happy with her serving, conceding just 11 points against eighth seed Gracheva off her serve and not giving up a single break point.

"I thought I served really well, probably the best so far at this tournament, which is something I was really working on in the off-season," the top seed Gauff said.

Fourth-seeded Navarro defeated the seventh seed Petra Martic 6-4, 6-3 in their quarter-final.

Navarro recovered from a slow start to break the Croat's serve six times and said she would need to bring the same level of aggression against Gauff.

The pair practised together this week, having not played each other since their early teens.

"She's an insane athlete. She covers the court super-well and is really solid in her whole game. There's no holes in her game," Navarro said of Gauff.

In the two other quarter-finals later on Friday, Ukrainian second seed Elena Svitolina faces fifth seed Marie Bouzkova while Wang Xiyu plays Diane Parry in a clash of two unseeded players.