The organisers said an audited attendance of 51,954 beat the 42,517 who watched Roger Federer play Alexander Zverev of Germany in Mexico City last November.
Australian Open final: Novak Djokovic is 6-4 in their career head-to-heads, but Dominic Thiem has won four of the last five.
Dominic Thiem came from a set down to outlast Alexander Zverev and make his first Australian Open final on Friday.
Alexander Zverev stormed into his first Grand Slam semi-final, rallying from a set down to shatter the dreams of Stan Wawrinka at Australian Open.
Stefanos Tsitsipas was in a different league to Alexander Zverev, who only began hitting balls a week ago after an off-season curtailed by a lucrative exhibition tour.
Dominic Thiem saw off the big-serving German 7-5, 6-3 after Greece's Stefanos Tsitsipas, making his ATP Finals debut, had earlier beaten Roger Federer.
Rafael Nadal exited the ATP Finals but ended his season as the world number one and with a chance to lead Spain to Davis Cup glory.
Rafael Nadal has never won the end-of-season tournament and had a miserable start at the O2 Arena, being outplayed by Germany's Alexander Zverev.
The "Big Three" remain the men to beat at the season-ending ATP Finals in London.
Alexander Zverev described his 7-6 (9/7), 6-4 loss to Taylor Fritz as 'flat' as he was knocked out of the ATP Swiss Indoors.
Daniil Medvedev defeated Alexander Zverev 6-4, 6-1 in the Shanghai Masters final
With Roger Federer and world number one Novak Djokovic ousted in the quarter-finals, the next generation of men's tennis stars has made its mark in China.
Roger Federer was penalised after twice hitting the ball out the court in anger.
Roger Federer delighted his home fans alongside Alexander Zverev, as the European pair saw off Shapovalov and Sock after a dramatic second set.
Rafael Nadal, second seed, produced some electrifying moments of brilliance to end the challenge of Croatia's Marin Cilic 6-3, 3-6, 6-1, 6-2 at the US Open.
Rafael Nadal, who won his fourth title in Canada a year ago, needed almost two hours on Friday to overcome the Italian veteran who shocked him on clay at Monte Carlo in April.
Andy Murray hasn't played singles since the Australian Open but says he might return at the ATP Cincinnati Masters starting August 12.
Alexander Zverev served nine double faults in a rollercoaster match, and survived two match points in the third set before ultimately losing in the tiebreaker.