In the opening match, Italy's Andreas Seppi rallied from two sets down to beat Vasek Pospisil 5-7, 4-6, 6-4, 6-3, 6-3.
Since he joined the Davis Cup team in 2010, the big-serving Raonic has been Canada's ace. He has earned six straight singles victories for Canada, and his overall Davis Cup record is 11-4, including 9-3 in singles.
In Saturday's doubles, Pospisil and veteran Daniel Nestor are scheduled to face Daniele Braciali and Paolo Lorenzi.
The winner of the Canada-Italy tie will move on to face either the U.S. or Serbia in the World Group semifinals in September.