Andy Murray lost in straight sets in the first round of the Canadian Open but fellow Briton Cameron Norrie progressed at the tournament in Montreal.
British number one Norrie, who lost in the final of the Los Cabos Open to Daniil Medvedev on Sunday, beat American Brandon Nakashima 6-4 6-4.
There were also wins for Britain's Jack Draper and Dan Evans.
After a 24-hour delay because of rain, Fritz - world number 13 and a quarter-finalist at Wimbledon last month - produced a dominant performance that several times reduced Murray to smashing his racquet against the court in frustration.