The Guimarães-born player, who himself ranks 62nd in the world, beat the 19-year-old Canadian 6-4, 6-7 (5-7) and 6-4, in a match that lasted two hours and 11 minutes. He did particularly well on his own serve, not facing a single break point.
Sousa, who last week reached the semi-finals in St. Petersburg, twice broke Auger-Aliassime’s serve: in the third game of the first set and in the 10th game of the third. That followed 26 games in which there were no break points on either side.
The Portuguese player thus knocked out a player who this year was a finalist in the Stuttgart, Lyon and Rio de Janeiro tournaments.
In the quarter-finals Portugal’s top player will face South Africa’s Lloyd Harris, ranked 111 in the world, who knocked out Serbia’s Dusan Lajovic, 29, with the score 6-3, 6-3. It will be the first time the two players meet in competition.