The American tennis great, Venus Williams, remains on course for the organisers' ideal ASB Classic final in Auckland against the top seed Caroline Wozniacki.
Williams beat Elena Vesnina 6-2 6-4 in their quarter-final yesterday, though the Russian caused the seven-time grand slam champion a few problems in the second set.
The 34-year-old says the challenge brought the best out of her.
Venus Williams faces her compatriot Lauren Davis in today's semi-final, after Davis staged another three-set comeback to knock out Polish qualifier Urzsula Radwanska 2-6 6-2 6-1.
Caroline Wozniacki is up against the Czech fourth seed Barbora Zahlavova Strycova in the other semi-final, after seeing off Julia Goerges in the quarters 6-4 6-4.
The Dane faces a very different opponent than the lanky German.
At just 1.64 metres tall, Zahlavova Strycova gives away 15 centimetres to Wozniacki, and at 28 is four years older - though the Dane isn't underestimating the challenge ahead.
"She is a very different player, she maybe doesn't possess the biggest power, but she places the balls really well, she has good hands, good volley skills, she's a good player and she's definitely improved in the last year I think. She has got more experience and I think with her age she has matured as a player."
The Wozniacki/Zahlavova Strycova match gets underway after 5pm, followed by the Williams/Davis semi.