The Spaniard and will face either Gael Monfils or Roberto Bautista Agut, who will close out the action under the lights at IGA stadium.
Nadal initially had a more tricky time in his quarter-final against Fognini, struggling with his serving accuracy in a first set where the Italian broke him twice.
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But Nadal broke to love in the second game of the second set on a double fault by Fognini, who appeared to be bothered by right ankle soreness as the nearly two-hour match wore on.
Nadal broke serve to start the deciding set and never looked back as he took a measure of revenge against Fognini, who defeated Nadal in the final of the Monte Carlo Masters in April.
The Spaniard said the key to getting back into the match had been staying in the moment.
Rafael Nadal in Montréal 2019
Image credit: Getty Images
"I lost 6-2, things went quick," he said.
"I started the second set thinking I was not playing bad, just things went so quick and everything against me," he said.
"I just tried to be there, to be focused and to calm down a little bit the match because things were going too quick."
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