The best match of the day lived up to the billing as Stan Wawrinka edged Nick Kyrgios in a thriller 1-6, 7-5, 7-5.
"It is one match, I know I have to learn from it", the fourth-seeded Kerber said.
Next up for Nadal is due to be Switzerland's Stanislas Wawrinka after he came from behind to beat Hungary's Márton Fucsovics 1-6, 7-6, 7-6.
The victory in just over two hours avenged a 2015 loss to Kyrgios in Canada, when the Swiss had to retire.
Kyrgios was at the centre of controversy in Canada three years ago when he alleged that fellow Australian Thanasi Kokkinakis had slept with Wawrinka's girlfriend, Donna Vekic.
"It's true that with my serve in the second set I had some troubles but my return was working well.it was more about the mistakes from the baseline in my opinion".
In second round play, Grigor Dimitrov survived a lengthy rain delay to turn away Fernando Verdasco in a final set breaker and in the early morning hours Marin Cilic got past countryman Borna Coric also in three.
Although former world No 1 Djokovic wasn't quite at his best he still had enough to dispatch the Bosnian 6-3 7-6 (7-3) in 90 minutes.
Japan's Kei Nishikori lost serve five times in a 7-5, 6-1 loss to Robin Haase of the Netherlands.
Also, Karen Khachanov of Russian Federation beat 12th-seeded Pablo Carreno Busta of Spain 6-4, 7-6 (7-3); Ilya Ivashka of Belarus topped American Ryan Harrison 7-6 (7-5), 6-4; and American Frances Tiafoe edged Canada's Milos Raonic 7-6 (7-4), 4-6, 6-1.
The first set of the clash was interrupted by rain which has plagued the Toronto tournament this week.
Azarenka punched her ticket to the second round with a dominating 6-0, 6-1 victory in just 55 minutes over the former world number 10.
Nadal, who clinched his eleventh French Open title this year, further said that he has now moved on from his narrow defeat to Djokovic and is now looking forward to the upcoming matches.
Zverev outclassed qualifier Daniil Medvedev 6-3 6-2. If you win, you play well in these two events and create this extra confidence to play well there, but if you lose it doesn't matter, the conditions are completely different", he added.
I had to learn that and understand that good things come with time and it takes time especially after surgery to hit thousands and thousands of balls and really get a comfortable feel on the court and eventually start playing well.
After beating a Top-20 opponent for the first time in his career Tuesday, the Montreal teenager is doing what he can to make his name more memorable.