Medvedev, a Russian national, is competing as a neutral athlete in Paris. He had won each of his previous seven matches against Auger-Aliassime, but they all took place on hard courts. The Olympic tournament is being played on clay.
The 23-year-old Canadian was also in action later Wednesday alongside Ottawa's Gabriela Dabrowski in the mixed doubles quarterfinals, facing the second-ranked American duo of Coco Gauff and Taylor Fritz. The fifth-ranked Canadians defeated Britain's Heather Watson and Joe Salisbury in their opening match on Tuesday.
Dabrowski and Laval, Que., native Leylah Fernandez were eliminated in the second round of the women's doubles tournament on Wednesday with a 6-4, 6-0 loss to neutral athletes Mira Andreeva and Diana Shnaider.
WATCH l Auger-Aliassime tops Medvedev in straight sets:
In men's action, 24-time Grand Slam champion Novak Djokovic defeated Dominik Koepfer of Germany 7-5, 6-3 to get to the Olympics quarterfinals for the fourth time. Djokovic won a bronze at the 2008 Beijing Games, but never has won a gold.
Djokovic now meets Stefanos Tsitsipas of Greece in a rematch of the 2021 French Open final. Tsitsipas took the first two sets that day, before Djokovic came back to win in five.
Olympics tennis uses a best-of-three-set format for all matches.
In other men's third-round results, Tommy Paul of the U.S. was a 7-6 (6), 6-3 winner against Corentin Moutet of France — the last tennis player from the host country in any Olympic event — and Taylor Fritz of the U.S. got knocked out of singles by Lorenzo Musetti of Italy 6-4, 7-5.
Entering Wednesday, Fritz was the only tennis player still in contention in three events, and he was scheduled to play three matches, including mixed doubles with Gauff and men's doubles with Paul.
Wimbledon champion Barbora Krejcikova of the Czech Republic bowed out of singles at the Paris Olympics with a 6-4, 6-2 loss to Anna Karolina Schmiedlova of Slovakia in the quarterfinals on Wednesday.
Schmiedlova has now eliminated both women who played in the final at the All England Club only 2 1/2 weeks ago. She defeated Wimbledon runner-up Jasmine Paolini in the third round Tuesday, and now is the first tennis semifinalist from Slovakia at a Summer Games since 1988.
Krejcikova was seeded ninth in Paris and has fared well on the clay courts at Roland Garros, which hosts the French Open and is the facility being used for tennis at these Olympics. Her first Grand Slam singles championship came at the French Open in 2021, when she also won the doubles title.
But with the heat at 90 degrees Fahrenheit (32 Celsius) and the air thick with humidity, Krejcikova looked listless down the stretch against Schmiedlova, a 29-year-old who is ranked 67th and owns one fourth-round appearance at a Slam. That came last year at Roland Garros.
By the end, Krejcikova appeared spent and was barely moving. She slapped a forehand into the net to finish the match, and Schmiedlova raised both arms overhead.
The two players accumulated nearly the exact same number of winners, with 18 for Krejcikova and 17 for Schmiedlova. But here's what was pivotal: the big difference in unforced errors — 32 by Krejcikova, more than twice was many as Schmiedlova's 15.
That included five double-faults for Krejcikova, who needed to deal with 11 break points and lost five of her service games.
Next for Schmiedlova will be a match Thursday against Donna Vekic of Croatia — who beat Coco Gauff in the third round — or Marta Kostyuk of Ukraine, with a place in the gold medal final on the line.
Iga Swiatek dropped to her knees on the court and clutched at her midsection after getting hit by a ball during a point in the Paris Olympics singles quarterfinals Wednesday, but it was her opponent, Danielle Collins of the United States, who stopped playing later in the third set.
Swiatek was leading 6-2, 1-6, 4-1 when Collins retired from the match after taking a medical timeout, then getting another visit from a trainer. It was not immediately clear what was wrong with Collins.
With files from The ' Howard Fendrich and The Canadian Press
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