Third seed Stefanos Tsitsipas' strong service game saw him overcome John Millman at the Stockholm Open, while teenager Denis Shapovalov also advanced in Sweden on Wednesday.

Tsitsipas, a two-time finalist on the ATP Tour this year, lost just eight points on his first serve in a 6-4 3-6 6-3 win over US Open quarter-finalist Millman that ensured he reached the last eight.

"I had a good start, got the break and thought it was a good start," the Greek said in quotes published on the ATP's website.

"I started playing defensively in the second set and got broken twice. It didn't affect me losing the second set, but I got closer to his serve in the third set and broke at 4-3."

Shapovalov, 19, won an all-Canadian clash with Peter Polansky 6-3 5-7 7-5 to record his 35th victory of the campaign.

"It was definitely a tough match, I knew it was going to be going in – having played him a few times earlier in my career," he said.

Jack Sock and Australian Open semifinalist Chung Hyeon also won their last-16 matches on Wednesday.

At the European Open in Belgium, French pair Gilles Simon and Richard Gasquet progressed but Milos Raonic was dumped out by compatriot Vasek Pospisil 7-6 (7-3) 7-5.

Feliciano Lopez is also out as Jan-Lennard Struff won the breaker in a 6-1 3-6 7-6 (7-3) success.

Top seed Marco Cecchinato fell at the Kremlin Cup as he was dispatched 6-2 6-3 by Adrian Mannarino, while Benoit Paire lost in straight sets to Egor Gerasimov.