Greece's Stefanos Tsitsipas battled back from a set down to defeat top seed Novak Djokovic 3-6 7-5 6-3 in the Shanghai Masters quarter-finals on Friday for his first victory over a reigning world number one.
The 21-year-old came into the match having sealed his place in next month's season-ending ATP Finals and celebrated with his second career win over Djokovic in three meetings.
Tsitsipas has now recorded victories over all of tennis's so called 'Big Three' this year, having beaten Roger Federer at the Australian Open and Rafa Nadal in Madrid.
"He had the high-quality tennis and he played well after his serve. He was backing up his serve with really good, aggressive first shots in the rally," Japan Open winner Djokovic, who came into the match on a seven-match winning streak, told reporters.
"I didn't make him defend enough. I just gave him enough time to really dictate the play from back of the court and he deserved to win."
Tsitsipas next faces Daniil Medvedev, who overcame Italy's Fabio Fognini 6-3 7-6(4). The Russian third seed's victory ensured Tsitsipas became the sixth player to qualify for next month's ATP Finals.
Djokovic, Nadal, Federer, Medvedev and Dominic Thiem have also booked their places in the Finals, with two spots still up for grabs for the tournament in London.
Roberto Bautista Agut and 2018 Finals winner Alexander Zverev, who is set to face Federer later in Shanghai, are currently in seventh and eighth places in the Race to London.