Third seed Venus Williams needed only to lift a gear to quell the budding threat of Russia's Elena Vesnina and win their quarter-final tennis clash at the ASB Classic.
The American third seed won 6-2 6-4 on Thursday in a match that ended in a hurry after a marathon 18-minute sixth game in the second set.
Williams, the world No.19, swept through the opening set of an encounter between two former Auckland finalists.
The unseeded Vesnina, who is ranked 64th, was far more competitive at the start of the second.
She got a break of serve to lead 3-2, then consolidated after an epic game that went to a dozen deuces.
But that merely galvanised Williams and the seven-time grand slam champion reeled off the last four games.
"That's really when I play my best, I think - when things get challenging, I get going too," she said.
"It's definitely a motivation."
In the semi-finals, she will face 21-year-old compatriot Lauren Davis, who got past Polish qualifier Urszula Radwanska 2-6 6-2 6-1.
It will be a first meeting between Williams and world No.54 Davis, a quarter-finalist last year.
On the other side of the draw, top seed Caroline Wozniacki progressed to the last four with a 6-4 6-4 win over Germany's Julia Goerges.
The Danish world No.8's consistency and patience proved decisive.
While Goerges unleashed some impressive winners, there were also costly unforced errors.
"I knew she was capable of coming up with huge shots from any part of the court and I knew I had to return deep and just take my chances," Wozniacki said.
"I just kept fighting. I tried to be more consistent than her and I managed to do that."
The win also marked a personal milestone for the 24-year-old Wozniacki.
"This is the first time I've reached the semi-finals to start the year, so it's already a good start for me," she said.
She will face Czech fourth seed Barbora Zahlavova Strycova, who beat American CoCo Vandeweghe 6-4 7-5.
No.7 seed Vandeweghe had led 5-2 in the second set, but couldn't serve it out to level the match.
Zahlavova Strycova, whose excellent serving included eight aces, capitalised to close out the contest, winning the next five games.
"It wasn't easy because I played a very powerful player and I had to focus, especially on my serves," the world No.26 said.
"I'm happy I pulled through the second set because the third set would have been very tough."
Zahlavova Strycova trails Wozniacki 3-1 head-to-head, but won their last meeting, in the fourth round at Wimbledon last year.
