Summary
Serena Williams beats Karolina Pliskova to reach semi-finals
American 17th seed wins 6-4 6-3 at Flushing Meadows
Argentina's Juan Martin del Potro through to semi-finals on Friday
Third seed beats John Isner 6-7 (5-7) 6-3 7-6 (7-4) 6-2
2017 champion Sloane Stephens knocked out by Anastasija Sevastova
Latvia's Sevastova through to semi-finals with 6-2 6-3 victory
Rafael Nadal plays Dominic Thiem in the last match of day nine
Extreme heat policy in place as New York temperature causes problems