Stirred by the assertion of the city's figurehead, singer Rita Lee, that Paulistas, as they are known, didn't know how to party in comparison to their cousins in Rio de Janeiro, the residents made sure that carnival came a month early.
At 18 million people - and growing - this grimy metropolis in the south of Brazil has little that is likely to waylay a tourist and suffers from a record 20% unemployment. But in a survey released this week, 83% of the city's residents said they were proud to live there.
Heading off to India for his 27th foreign trip since he took power a little over a year ago, President Luiz Inacio Lula da Silva, dropped in to inaugurate South America's biggest fountain in the central park, Ibirapuera, on the eve of the anniversary.
The day itself, 25 January, began at the stroke of midnight - under a downpour - with Caetano Veloso singing Sampa, his 25-year-old eulogy to the city, standing on the corner of Avenida Ipiranga and Sao Joao, streets made famous in the lyrics of the song. "The solution for Brazil is the happiness of Sao Paulo," said the artist.
At daybreak the last-minute preparation of 31 sound systems aboard trucks was complete and the convoy then thundered down one of the city's main roads, 23 of May, which was closed to its normally less glamorous gridlock.
Free haircuts, yoga, zen practice, stations with free phone calls to any part of the country, children's play areas were all on offer and tickertape littered the road. On closer inspection the tickertape turned out to be inscribed with lines of famous Brazilian poetry - and Shakespeare.
An estimated 2.5 million people took to the road, dancing to Sao Paulo's fashionable version of drum & bass and techno. Organisers claimed it was the biggest party ever seen in the city – exceeding 1.9 million people on New Year’s Eve.
"This is the greatest city in the world and this is the best party ever," said 19-year-old Ana-Paula. Her friend, Fabiana, hundreds of others, contented herself by dancing deliriously from sound system to sound system encouraging those in the trucks to even higher levels of exaltation.
"This is the greatest city in the world and this is the best party"
At the birthplace of Sao Paulo, the Patio do Colegio, a civic reception opened the ceremonies. In local election year, the anniversary party was a coup for the current mayor, Martha Suplicy, who also inaugurated a new town hall on the same day. The event cost $1.5 million, the majority borne by a single mobile-phone operator.
"It's a bit of a false celebration in truth. Of course it is political," said Ze, 46. "But it's a lot of fun anyway!"
Mass was held at Se Cathedral - a poignant marker and point zero in the city which was the focus of massive demonstrations for the right to vote in 1984, which helped to oust the then 20-year-old military regime.
Buildings were gift-wrapped in red ribbons, banners carrying the heart-shaped 450-years logo were draped from skyscrapers, plastered on T-shirts, hats and most spectacularly drawn in the sky by the Brazilian air force.
Around 2,000 people in the Italian district, Bixiga, devoured a world-record-breaking 450m long cake in an estimated 25 seconds.
National TV channels suspended all programmes for round-the-clock coverage.
Love and peace
The military police said there were no serious incidents - extraordinary in a city plagued with crime; Sao Paulo registered more than 4,000 murders last year alone.
By late afternoon Brazil's famously changeable climate offered the partygoers torrential rain. Heavy rain had already led to a spate of deaths within the state during the week as emergency services struggled to deal with seasonal storms.
Party in the park: Crowds gather
to celebrate before the storm
Umbrella-sellers rapidly sold out but the record-breaking crowds carried on regardless. Rivers ran down the streets while the masses splashed onwards in the dark, by now abandoning futile attempts to cover themselves with plastic bags and newspapers.
Almost half a million people stayed to see the day out, the finale being a firework display on the symbolic Avenida Paulista - the richest street in South America - and the open-air spectacular headed by the doubting Rita Lee.
"I have lived here for 56 years. How can I say anything bad about Sao Paulo?," she screamed to the crowd. "Viva Sao Paulo!"