Roger Federer said that his devoted band of Chinese supporters helped pull him through a tough first set and into the Shanghai Masters quarter-finals on Thursday.

The Swiss defeated David Goffin 7-6 (9/7), 6-4 after the 13th seed from Belgium squandered five set points in the first set.

The 38-year-old Federer plays Alexander Zverev after the young German beat Andrey Rublev of Russia, 6-0, 7-6 (7/4).

"I never really felt like I had the upper hand against David today," said the 20-time Grand Slam winner, who looked unusually flustered at times.

Federer was left shaking his head in the first set and he suffered a rare inelegant moment in the 12th game, slipping on his own sweat - "a bit embarrassing," said the former No. 1.

The Swiss fell awkwardly and was then broken by Goffin, 14th in the world.

But the Belgian lost his nerve despite going 3-1 up in the first-tie break, and Federer roared back to turn the momentum in his favor.

Federer was regularly serenaded by chants of "Roger, Roger, go go go" by local supporters all sitting together in one part of the arena. All were decked out in red.

Federer, who failed to win a Grand Slam this year, said their backing had been key to his revival.

"It's definitely very special here because they all sit in one block, sort of like in football to some extent, which is highly unusual for tennis and a tennis tournament," he said.

Federer, fondly nicknamed "cow" in China, will play an exhibition tournament at the end of the year in the nearby city of Hangzhou, east China's Zhejiang Province.

"Hangzhou was just something I thought would be this year good preparation for the Australian Open and also something that would be very exciting for me to go and play," he said.

World No. 1 Novak Djokovic made light work of American John Isner and plays promising 21-year-old Stefanos Tsitsipas of Greece in the last eight.

The defending champion from Serbia dismissed the 16th seed Isner 7-5, 6-3 in 74 minutes after taming Isner's booming serve.

"It's always a big challenge returning the serve of Isner," said Djokovic, who is over the shoulder problem that curtailed his U.S. Open defense.

"He's got one of the biggest serves of all time, he's one of the tallest guys ever to play tennis."

The 32-year-old Djokovic is looking imperious, having not dropped a set in claiming the title in Tokyo last week and continuing that perfect record in Shanghai.