Jessica Pegula upset Aryna Sabalenka in straight sets at the WTA Finals in Cancun on Tuesday, punishing an error-strewn performance by the World No. 1 to reach the semi-finals of the season-ending tournament for the first time. World No. 5 Pegula, who had beaten Sabalenka only once before in five previous meetings, dominated her out-of-sorts Belarusian opponent from the outset to claim a 6-4, 6-3 victory. 

Jessica Pegula