SHANGHAI -- Canada's Denis Shapovalov and Felix Auger-Aliassime lost second-round singles matches Wednesday at the Shanghai Masters.

Shapovalov, from Richmond Hill, Ont., dropped a 6-3, 6-3 decision to top-ranked Novak Djokovic while sixth-seeded Stefanos Tsitsipas beat Auger-Aliassime 7-6 (3), 7-6 (3) for the Greek's first win in six attempts over the Montreal player.

The pair have met three times this season, with the other three games on the ITF junior circuit.

"Great. Very nice," said Tsitsipas, when asked how it felt to finally beat the 19th-ranked Auger-Aliassime. "I did things differently this time, but I prefer not to say what I did differently."

Djokovic is the top seed and defending champion at the ATP Tour event.

"It's nice to be back," he said. "And also, it feels very good to play as well as I did today. I knew that Denis is very dangerous player. If he has time, if he's feeling the ball well, it can be a tough match."

The 36th-ranked Shapovalov struggled with his service game, hitting only 53 per cent of his first serves. Djokovic, who hit 74 per cent of his first serves, needed one hour 10 minutes to complete the victory.

In doubles play, Auger-Aliassime and Italy's Matteo Berrettini posted a 6-7 (4), 7-6 (5), 10-4 first-round victory over Croatia's Nikola Mektic and Franko Skugor.

Fifth-seeded Alexander Zverev advanced to the round of 16 with a 7-6 (13), 7-6 (3) win over French qualifier Jeremy Chardy. Zverev, who served 21 aces, saved three set points in the first-set tiebreaker. He won that tiebreaker on his sixth set point.

"It was a great tiebreaker obviously," Zverev said. "We both served incredibly well and didn't hit a lot of second serves ... Against Jeremy I always knew it was going to be tough especially on a surface like that, which is lightning fast. I think it's the fastest surface on tour."

Chardy has now lost 11 consecutive matches against top 10 opponents dating back to when he defeated then fourth-ranked Grigor Dimitrov of Bulgaria at the 2018 Miami Masters.

American John Isner beat Lucas Pouille of France 7-5, 6-3 and American Taylor Fritz fell to seventh-seeded Karen Khachanov of Russia 6-2, 6-4.

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With files from The Canadian Press