Tennis: Coco Gauff continues dominant ASB Classic title defence, powers into semi-finals in straight sets

Top seed Coco Gauff's emphatic defence of the ASB Classic has continued, as the American booked a semi-final spot in just shy of 54 minutes with a straight sets victory over Varvara Gracheva.    

The 19-year-old continues to be untroubled by her opposition at this year's tournament, one year on from lifting the trophy at Stanley Street.   

This time, it was eighth seed Gracheva who met her exit at Gauff's hand in the quarter-finals, as the American sent down five aces and broke serve five times en route to a second successive semi-final in Auckland.    

After a short delay to the afternoon's second match thanks to light rain, Gauff started strong by holding serve twice and breaking Gracheva at the first attempt for a 3-0 lead in the opening set.

Gracheva was able to stop Gauff's momentum, slightly, by holding serve in the fourth game, only to be broken again shortly after and give the top seed the chance to take the first set. 

And having not dropped a set at Stanley Street over the past two tournaments, Gauff didn't relent to take the first inside half an hour.   

Another two Gauff breaks followed to start the second set, before Gracheva managed to hold, albeit at 4-1 down.    

Undeterred, Gauff held yet another to go 5-1 up and leave Gracheva having to hold to avoid defeat.   

To her credit, Gracheva was able to save two match points, but Gauff didn't waste the third, and broke serve one last time to complete a 6-1, 6-1 victory inside an hour.   

Earlier, fourth seed Emma Navarro became the first player into the final four, courtesy of a straight sets victory over seventh seed Petra Martic.   

In just under 90 minutes, Navarro sent down two aces and broke serve five times to take a 6-4, 6-3 win and set up an all-American encounter with Gauff for a place in Sunday's final.   

The two remaining quarter-finals, where China's Xiyu Wang will meet France's Diane Parry and second seed Elina Svitolina and Czech Republic's Marie Bouzkova face off, will be played on Friday night.