Defending champion Petra Kvitova booked her spot in the semi-finals of the Connecticut Open after beating seventh seed Agnieszka Radwanska 7-5, 6-4 on Thursday.
Kvitova, who beat Magdaléna Rybáriková in last year's final, continued her impressive run at the event at which she has made the semi-finals for the past four years, having also taken home the title in 2012.
The Czech did not get off to the best of starts and was broken by Radwanska early in opening game of the match. She broke back immediately, but soon found herself 5-3 down after surrendering a second break.
However, the second seed fought her way back into contention by breaking Radwanska in the 10th game and again in the 12th game to take the set.
Kvitova and Radwanska broke each other in the first two games of the second set before holding serve for the next seven games. With Kvitova leading 5-4 she broke Radwanska once more to take the set and with it the match in an hour and 41 minutes.
Kvitova will face four-time champion Caroline Wozniacki in the last four after she cruised past Caroline Garcia 6-3, 6-0.
Wozniacki was unstoppable and broke Garcia five times, while also winning 70 per cent of her points on her first serve, to beat the Frenchwoman in just 54 minutes.
In the second semi-final, Lesia Tsurenko will face Lucie Safarova after getting the better of world number eight Karolina Pliskova 6-2, 6-2. In the day's other early quarter-final, Safarova came from a set down to beat Dominika Cibulkova.