Serena Williams has continued her winning streak at the Auckland Open after she defeated Germany's Laura Siegemund in straight sets to reach the semi-finals. 

The multi Grand Slam champion beat world No 73 Siegemund 6-4, 6-3 . She will face either Amanda Anisimova or Eugenie Bouchard in the last four. 

Despite reaching the semis, Williams had five break point chances and converted only three but did however hit six aces. 

The German who ended 15 year-old Coco Gauff's progrress, failed to match the top seed's power from the baseline. 

Afterwards, Williams said: "She was an incredibly tricky player and the conditions really didn't help.

"The body's feeling great. I came in here before the tournament last year and said I wanted to play singles and doubles here. So I'm happy, I knew what I was going to be up against and I'm happy to still be in the tournament."

Elsewhere, Caroline Wozniacki progressed into the semis with a 6-1, 6-4 victory over the two-time defending champion and fourth seed Julia Gorges. 

The Dane, who is set to retire after the Australian Open, will play US qualifier Jessica Pegula.

Star duo Wozniacki and Williams play their doubles semi-final against Belgian pair Kirsten Flipkens and Alison van Uytvanck later today.