Agnieszka Radwanska overcame Olympic champion Monica Puig 6-2 6-3 to reach the semi-finals of the Pan Pacific Open, where she will face Caroline Wozniacki.
Two-time defending champion Radwanska needed three sets to overcome Barbora Strycova in the second round, but proved more controlling in her last-eight clash with Puig.
The world number four dominated her opponent's serve and produced eight aces, conceding just three points on her own in the opening set.
Although Puig cancelled out an early slip to draw level at 2-2 in the second set, the Pole broke her to love twice further.
Next up for Radwanska is Wozniacki, who booked her place in the semi-finals by defeating Magda Linette 6-4 6-3.
Wozniacki missed a chance to break for the opening set at 5-3 and followed it by dropping her serve, but she immediately broke back to move one set up.
A tight second set saw four breaks in the first six games, but the Dane showed her experience to win each of the next three to complete the victory.
Elina Svitolina eliminated French Open champion Garbine Muguruza 6-2 4-6 6-3 in a match lasting over two hours.
Svitolina raced into a 5-0 lead and required four set points before moving ahead, but Muguruza forced a decider with a single break point all she required.
Tension was high and it was the Ukrainian who came out on top, winning a pivotal game at 4-3 in the third set.
Wildcard Naomi Osaka will face Sviotlina in the semi-finals after overcoming Aliaksandra Sasnovich 6-3 7-6 (8-6).