The second-seeded Murray struggled at times but outplayed the Spanish surprise winner of last week's Kitzbuhel event by a 6-4, 7-6 (7-2) margin at Stade Uniprix in Montreal.
The triumph was the 13th straight for the two-time Canadian Masters champ, who last month became the first British male Wimbledon singles winner in 77 years.
His next opponent will be Latvian Ernests Gulbis, who advanced with a 6-3, 1-6, 6-1 defeat of 13th-seeded Italian Fabio Fognini.
Nadal showed few signs of rust in his initial match since taking an early exit at Wimbledon in late June.
In other Day 3 matches, No. 5 Czech Tomas Berdych, Frenchman Benoit Paire and Australian qualifier Marinko Matosevic each posted a victory.