The eighth-seeded Medvedev needed only 57 minutes to beat Thiem, whose transition to the hard court season was made more difficult because he arrived here on Sunday after winning a tournament on clay in his native Austria.
Two-time Roland Garros finalist Thiem, who had never won a match in Canada over five years of trying before this week, said he did not have a chance against Medvedev as a hectic travel schedule caught up with him in his 56-minute loss.
"I was not playing bad", the top seed and No. 2 player in world said of the deficit.
"I lost things on the road, so I just tried to add other things", Nadal said.
With the win, Nadal made the Rogers Cup semis in Montreal for the first time since 2013 when he beat Canada's Milos Raonic in the final.
I mean, I made the best American swing I could have made past year, and it was only going up, and she does a lot for me in order for me to play better tennis. It saved me a lot of energy.
Russian Daniil Medvedev was among the most consistent players in the early part of the season and at one point had the best record for the year on the tour.
Medvedev's best result at the Grand Slam tournaments is the fourth round of the 2019 Australian Open, he has won four ATP titles. "I was not. 100 per cent".
In June, Khachanov became the first Russian to be ranked in the top-10 since Mikhail Youzhny in February 2011, and Medvedev joined him last month.
The No. 6 seed had to work only a bit harder than Medvedev, since he upset the 2017 Rogers Cup victor, third-seeded Alexander Zverev of Germany, 6-3, 6-3 in one hour and 14 minutes.
"It's never easy to play a good friend, especially from the same country", Khachanov said.
"It was obvious that when you play against local guy, Canadian, the crowd would be mostly on his side", Khachanov said. "We know each other pretty well".