Fresh from defending his Japan Open title with a victory over Czech Jiri Lehecka and building momentum after a lengthy wrist injury layoff, Alcaraz never found his rhythm in a scrappy two-hour, two-minute contest.
The second-seeded Spaniard, who was sidelined for nearly five months before returning at the US Open in late August and reaching the quarter-finals, joined 24-time Grand Slam champion Novak Djokovic and US Open runner-up Ben Shelton among the high-profile casualties at the ATP Masters 1000 event.
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Bergs produced a composed all-court performance, thriving in the quick conditions as the 27-year-old broke Alcaraz's serve three times to clinch the biggest victory of his career.
Bergs had lost their only previous meeting, falling to Alcaraz in the last 16 of last year's Japan Open, but showed no signs of intimidation as he outplayed the 23-year-old in key moments.
"This is something that has been very tough for me," Bergs said, when asked about getting a win against one of the biggest names on the ATP Tour.
"I often have too much respect for these guys, which is part of my culture and I'm proud of that. But it gets a little bit in the way when you have to play them...
"The more experience you have practising against them and playing matches, the more it becomes the new standard a little bit. To have this moment, for me it is a little bit of a relief. I feel like now I really can win against these guys..."
'Dream come true'
The upset also guaranteed French Open and US Open champion Zverev, 29, the ATP's year-end world number one ranking, making him the first German and the oldest first-time player to achieve the feat.
Zverev's route to the top spot opened after Italian Jannik Sinner had not played since beating him in the Wimbledon final on July 12th due to a knee injury.
The 25-year-old missed the North American hard-court swing, the US Open and the ongoing Asian swing. The five-time major winner will also sit out the European indoor season and the ATP Finals in Turin, where he has lifted the trophy in each of the last two years.
"It's been a fantastic season for me, winning in Paris and New York and knowing that I will finish the year on top of the rankings is just a dream come true," said Zverev, who will face Kazakhstan's 19th seed Alexander Bublik in the round of 16 in Shanghai.
"So much work and effort have been put into achieving this goal, especially after coming back from the ankle injury (at the 2022 French Open semi-finals).
"I look forward to finishing the season in style."
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