Thousands of people were turned away after 14,065 others managed to cram into El Zocalo square. About 23,000 had officially registered for the event.
"We expected about 13,000 players and we have 23,000 registered," said the city's Mayor, Alejandro Encinas, as he made the first move on a giant chess board.
Organisers said the attempt beat the current Guinness record, which was set in nearby Pachuca, Mexico, in June 2005, by nearly 1,700 players.
They must await confirmation from the Guiness organisation before the record can be amended.
People with a range of abilities took part and 602 masters took on as many as 24 opponents at a time.
Anatoly Karpov, the former world chess champion, was among national champions and several grand masters who joined in.
"This is fantastic," he said. "It is so important to give all these talented kids a chance to improve their chess so they can have success in the future."
Guinness says Mexico also holds the record for the longest-running television cooking show, Hasta la cocina, which began in 1960, as well as the largest number of calves to one cow in a single birth.
The Guinness Brewery launched the book in 1955 to settle disputes among beer drinkers about world records.