REUTERS: Wimbledon champion Novak Djokovic defeated American Steve Johnson 6-4 7-6(4) in a hard-fought match under the lights.
The 31-year-old Serb is searching for his first Cincinnati Masters title after five finals.
Swiss Stan Wawrinka dug deep and ultimately prevailed 6-2 4-6 6-3 against twelfth seed Diego Schwartzman in their first career meeting to set up a highly-anticipated battle with Japan’s Kei Nishikori.
Spain’s Pablo Carreno Busta, Briton Kyle Edmund and Canadian young gun Denis Shapovalov also advanced to the second round.
The tournament lost its top seed when world number one Rafael Nadal withdrew after winning the Rogers Cup on Sunday.
World number two Roger Federer, who skipped the Toronto event, is now the highest seed.