In the men’s event, taking place in Toronto, Alexander Zverev battled back from a set down to beat defending champion Alexei Popyrin 6-7 (6-8) 6-4 6-3.
The 28-year-old German is into his 75th semi-final on the ATP Tour, becoming the only active men’s player to have reached that milestone alongside Novak Djokovic.
He will face Russian Karen Khachanov, who moved past Alex Michelsen of the United States 6-4 7-6 (7-3).
The Cincinnati Open confirmed Djokovic had withdrawn for “non-medical” reasons from the tournament, which begins on Thursday.
The 24-time Grand Slam champion, who is not competing in Toronto because of a groin injury, has not played since losing to Jannik Sinner in the semi-finals of Wimbledon.
The 38-year-old is unlikely to play before the US Open, which starts on 24 August.
