French veteran Gael Monfils stunned fourth seed Stefanos Tsitsipas at the ATP Toronto Masters on Wednesday, winning in straight sets to advance to the last 16.

The 36-year-old from Paris -- currently ranked 276th in the world -- powered past Tsitsipas 6-4, 6-3 in just under 90 minutes.

The win marked the first time Monfils has beaten a player in the top 10 since March 2022, and came against an in-form Tsitsipas fresh from winning the ATP Los Cabos title in Mexico last weekend.

Monfils, who reached the Washington third round last week, overcame 29 unforced errors to advance.

It took two match points for Monfils to get the job done, with a shotmaking duel on the first winning chance ending in Tsitsipas' favour before the French veteran closed out victory moments later.

"After (losing) the first match point, I stayed very calm and tried to make simple choices," Monfils said.

"Maybe I was a bit too simple on the first match point, but I just stayed cool, there was no panic.

"I knew Stef came here with a lot of confidence and would be going for his shots."

Elsewhere Wednesday Daniil Medvedev advanced to the third round with a 6-2, 7-5 win over Matteo Arnaldi.

Medvedev said he needed to make more of an effort in the second set in the steamy summer conditions against Arnaldi. He struck 26 winners and 18 unforced errors.

"It felt great, but I could have played better in the second set," Medvedev said. 

"There were two or three games where I had to save break points.

"It was a pretty good match, now I need to improve further.

"It's hot conditions during the summer and I need to get used to them. That usually takes two or three games."

Medvedev improved to 8-1 in Toronto with his victory, his 47th this season.

Sixth seed Andrey Rublev stumbled in his first hardcourt match of the summer, losing 6-4, 6-3 to American Mackenzie McDonald.

Canadian Milos Raonic, returning to the Tour after two years of injuries, continued to advance as he beat Japan's Taro Daniel 6-4, 6-3.

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