Gael Monfils rolls back the years to shock Stefanos Tsitsipas in Canada
The flamboyant former top-10 star has struggled with injuries over the past year and is ranked down at 276 but showed he still possesses the skills to trouble the very best with a 6-4 6-3 victory over fourth seed Tsitsipas.
The Greek, who won a title in Mexico last weekend, made a lot of mistakes, particularly on his forehand wing, but Monfils, three weeks short of his 37th birthday, was excellent in defence and attack.
Home favourite Milos Raonic continued his resurgence, meanwhile, following up his upset of Frances Tiafoe by seeing off qualifier Taro Daniel 6-4 6-3.
The former Wimbledon finalist did not compete between July 2021 and this June because of injuries and is unsure what the future holds but he has made it back-to-back victories at the Canadian Masters event for the first time in seven years.
He next faces American Mackenzie McDonald, who knocked out sixth seed Andrey Rublev 6-4 6-3, while second seed Daniil Medvedev is safely through after a 6-2 7-5 win over Matteo Arnaldi.