Adelaide - Two-time Grand Slam winner Simona Halep will head into the Australian Open with room for improvement after being upset 6-4, 6-2 by Aryna Sabalenka on Thursday at the ATP-WTA Adelaide International.
The reigning Wimbledon champion and former world No 1 dropped serve five times and was flattened in the second set by her opponent from Belarus.
The 71-minute rout leaves Halep standing 1-1 for the season with the first Grand Slam of the year starting on Monday in Melbourne.
Sabalenka will battle Dayana Yastremska on Friday for a place in the final after the Ukrainian 19-year-old beat a second top 20 opponent this week when she put out Croat Donna Vekic 6-4, 6-3.
Sabalenka, ranked 12th to Halep's fourth, won her first match after two losses to the Romanian, coached by Australian Darren Cahill.
"It feels great, we had a tough match and she played well," Sabalenka said. "I
tried to stay focused on each point. I don't care about the Grand Slam, I'm just playing each match."
"I didn't care about the past, I stayed in the moment, that helped me to win."
In the first set, Halep twice lost break advantages, with Sabalenka coming through with a third break of serve in the final game on a double-fault from the seed.
In the second, the Belarussian ran away with it - Halep drew applause and raised her arms in mock triumph as she finally won a game while trailing 5-0, but the youngster fired a winning return to seal match point.
Yastremska, ranked 24th, was thrilled to get past Vekic.
"It's nice to be in the semi-finals just in the beginning of the year," she said.
"I'm not playing my best game, but it's still nice."
"I'm just getting my form. I have a big goal for Australia, but I'm going to try to stay really realistic and play match by match. That's all I can think about."
Last year's 2019 Australian Open semi-finalist Danielle Collins crushed fourth seed Belinda Bencic, sending the Swiss out in barely an hour with four breaks of serve.
The 27th-ranked American will play either Australian top seed Ashleigh Barty or Marketa Vondrousova next.
In men's play, South African Lloyd Harris beat Spanish fourth seed Pablo Carreno Busta 6-3, 6-3 to book a semi-final berth.
He will play a fellow qualifier after Tommy Paul advanced over Spain's Albert Ramos-Vinolas 6-3, 6-4.
Russian third seed Andrey Rublev won his sixth match of the season, with last weekend's Doha champion defeating Britain's Dan Evans 6-4, 3-6, 6-3.
Results on day five of the ATP-WTA Adelaide International at Memorial Drive:
Lloyd Harris (RSA) bt Pablo Carreno-Busta (ESP x4) 6-3, 6-3
Tommy Paul (USA) bt Albert Ramos (ESP) 6-3, 6-4
Andrey Rublev (RUS x3) bt Daniel Evans (GBR) 6-4, 3-6, 6-3
Dayana Yastremska (UKR) bt Donna Vekic (CRO) 6-4, 6-3
Aryna Sabalenka (BLR x6) bt Simona Halep (ROU x2) 6-4, 6-2
Danielle Collins (USA) bt Belinda Bencic (SUI x4) 6-3, 6-1