Serena Williams powered past Romania's Simona Halep to set up a semi-final with Li Na in the Cincinnati Open.
The world number one, seeking her ninth title of the year, took only an hour and four minutes to win 6-0 6-4.
Defending champion Li had a walkover against Agnieszka Radwanska, who returned to Poland to attend a funeral.
Second seed Victoria Azarenka eliminated Caroline Wozniacki 6-3 7-6 (7-5) and will play Serbia's Jelena Jankovic in the other last-four tie.
Williams, 31, raced through a 16-minute opening set against Halep, who had beaten
Marion Bartoli in the second round. It was the Frenchwoman's last match before she
announced her retirement.
A dominant Williams broke serve five times in total and sent down six aces to make the last four of a tournament she has never won.
"I definitely haven't felt that good all week, so I'm surprised I'm still in the tournament to be honest.
"At the end it's not really about how you play, it's about being able to win, whether you're playing well or not. So far I've been able to be in the semi-finals. It's a good result."
Azarenka's win was only the Belarussian's third in nine meetings against Denmark's Wozniacki.
Jankovic beat Italy's Roberta Vinci 6-0 6-4.