Illness forced 2018 champion Damir Dzumhur out of the Antalya Open, while two-time runner-up Adrian Mannarino was beaten in three sets.
Felix Auger-Aliassime will battle with compatriot Milos Raonic for a place in the final of the Stuttgart Open.
Alexander Zverev is 165 places above Dustin Brown in the rankings, but lost to his compatriot on home soil in Stuttgart.
Spanish veteran David Ferrer celebrated his 728th career win following Tuesday's victory against Malek Jaziri.
Martin Klizan needed a third-set tie-break to get past Alexei Popyrin at the Sydney International.
There was a Russian winner at the 2018 ATP Kremlin Cup as Moscow-born Karen Khachanov cruised past Adrian Mannarino.
Adrian Mannarino had gone two months with a win, but reached the second round in Moscow on Monday.
Novak Djokovic was seen by medical staff at the Cincinnati Masters but then reeled off six successive games in beating Adrian Mannarino.
Kyle Edmund earned his first Cincinnati victory by defeating Mackenzie McDonald 6-3 6-2 on Sunday.
A three-time finalist at the Hall of Fame Tennis Championships, Ivo Karlovic suffered a second-round loss.