Madison Brengle was unable to keep up the momentum after beating Serena Williams, suffering elimination at the ASB Classic a day later at the hands of Jelena Ostapenko.
Brengle made the most of blustery conditions to oust the former world number one in three sets on Wednesday, but seventh seed Ostapenko proved an obstacle too far in the quarter-finals, the Latvian winning 7-5 6-3.
Ostapenko will play Lauren Davis in the final four after the American was a 6-1 7-6 (7-4) victor over fourth seed Barbora Strycova.
Both Serena and Venus Williams have faltered in Auckland, and the shock theme continued on Thursday as Julia Goerges pulled off a stunning comeback win 1-6 6-3 6-4 against former top-ranked player Caroline Wozniacki.
Wozniacki appeared to be cruising to victory a set and two breaks to the good at 3-0 in the second, but Goerges reeled off six straight games with some wondrous shots on the back foot.
With impetus firmly behind her, Georges raced into a 5-1 lead in the decider and saw out the victory after Wozniacki threatened a late revival.
Ana Konjuh is Goerges' semi-final opponent after Naomi Osaka withdrew injured against the Croatian after just two games.