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