Gauff, Svitolina power 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.

Ukraine's Elina Svitolina later dispatched Marie Bouzkova 6-0, 6-3 to ensure the tournament's two top seeds advanced on a day in which rain played havoc with the four quarter-finals.

With 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 conceding just 11 points against eighth seed Gracheva against her serve, without 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.

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.

Second seed Svitolina's match finished at close to 11pm local time and the 17-time WTA singles title winner was pleased to make short work of fifth-seeded Czech Bouzkova in cold conditions.

"It was a great performance from me and I'm surprised how many people are still here," she said.

"I wanted to make it short and sharp so I'm happy with my level that I could actually win and not expend too much energy."

The three-time Grand Slam semi-finalist will next face China's Wang Xiyu, who fought back to beat Diane Parry 6-7 (3/7), 6-3, 6-4 in a clash of two unseeded players.