Halep overcame the Czech, who produced the most aces last season on the WTA, for the third time without loss after defeating her twice in 2015.
“It was a tough match,” Halep said. “She plays very strong, hits very hard and has a great serve. I had to try everything to win today.
“I’m happy to win in two sets,” Halep added after eliminating last year’s finalist. “It’s my first semi-final this season.
“I’ve played Kuznetsova many times and I expect a tough match. She has another style but I’ll be ready.”
Swiss eighth seed Belinda Bencic broke new ground to secure a final-four appearance through a defeat of Ekaterina Makarova 6-0, 2-6, 6-4 while Puerto Rican qualifier Monica Puig continued a fairytale week by beating Australian warrior Samantha Stosur 6-4, 6-4.
Halep was broken in the eighth game of the second set after holding an early break of her own but produced a re-break of Pliskova for 6-5 before serving out victory a game later on her second match point.
In men’s play, Australian top seed Bernard Tomic reached the quarters of the ATP-WTA tournament as he thrashed teenaged compatriot Jordan Thompson 6-2, 6-2 in 49 minutes, losing just seven points on serve in the rout.
“It was not that easy as I’ve barely hit with him and have not trained with him for a few years,” the winner said. “It was difficult to get into the match.
“I’m happy with my form, I played consistently last week in Brisbane and I’m very confident. That’s an important thing.
“Sydney is my favourite event, it’s where it all got started for me (with his debut title in 2013).”
Tomic next plays Teymuraz Gabashvili, a winner over Federico Delbonis 6-3, 6-3.
Veteran Gilles Muller schooled second seed Dominic Thiem, winning 7-6 (7-2), 2-2 when the Austrian retired. Holder and third seed Viktor Troicki hammered Spain’s Tommy Robredo 6-1, 6-4.
Fourth seed Grigor Dimitrov continued his renaissance this season, defeating Pablo Cuevas 7-6 (7-2), 6-4.
Nicolas Mahut upset Italian fifth seed Andreas Seppi 6-3, 1-6, 6-3, sixth seed Jeremy Chardy beat James Duckworth 7-6 (7-5), 6-4 and Hopman Cup finalist Alexandr Dolgopolov stared with a victory as eighth seed over Alexander Sarkissian 7-6 (8-6), 6-2.