FIFA Secretary General Jerome Valcke has said Sao Paulo's delayed stadium would be ready "at the last minute" for the World Cup curtain-raiser on 12 June after a full capacity test next month.
The stadium has suffered delays following two fatal accidents that left three workers dead, but Mr Valcke said he was confident preparations were advancing well.
"Sao Paulo will be ready for the opening match", between Brazil and Croatia, said Mr Valcke, adding there was "no choice" while repeating his mantra that "we cannot waste a single minute".
Mr Valcke told reporters: "We are running against time, but yes, the stadium will host the opening game and, yes, we will organise the opening game and all the other games in this stadium."
The stadium will host six games in total, including a semi-final.
He had earlier tweeted: "(The) next important event for us will be on 17 or 18 May when the first official test with full capacity will take place at Arena de So Paulo."
With FIFA normally wanting three tests at venues, Mr Valcke indicated that Sao Paulo therefore faced "a very tight schedule" through to the 12 June kick-off.
He insisted he was "happy with progress" as "TV area & IT installations (are) taking shape, accreditation & volunteer centres open in 3 weeks".
FIFA set an initial deadline of 31 December for all 12 venues to be ready.
Sao Paulo was then put back to 15 January, but delays have continued to dog the project.
Fatal accidents at the venues of Brasilia and Manaus killed another four workers, while other delays have beset Porto Alegre, Cuiaba and Curitiba.
Mr Valcke started off his latest monthly trip to Brazil by visiting Sao Paulo's Corinthians Arena, which he called a "beautiful football arena", ahead of trips to Curitiba, Cuiaba and Fortaleza through to Thursday.
Constructors symbolically handed over the Sao Paulo stadium, which is still unfinished, to owners Corinthians last week ahead of its expected delivery to FIFA on 20 May.
Mr Valcke then visited the southern city of Curitiba to inspect the Baixada Arena, which he threatened to leave off the venue list until February, when it was reprieved after work on the venue was stepped up.
Tomorrow will see Mr Valcke in the central city of Cuiaba, whose stadium is also unfinished, before he heads down to Porto Alegre, where the stadium is ready except for temporary structures.
In Fortaleza on Thursday, Mr Valcke is scheduled to visit the Aterro de Iracema site, which is due to host the Fan Fest, or open air street party area for fans without tickets.
Meanwhile, AFP has reported violent protests in Rio de Janeiro's tourist heart of Copacabana following the death of a resident.
The violence comes less than two months before the city hosts seven games at the World Cup.
Two main thoroughfares were closed after angry demonstrators set ablaze barricades of tyres.
They were protesting against the death of a dancer who was believed to have been killed by a police unit who mistook him for a drug trafficker.