Last year Red Bull won all but one of the season's 22 grands prix, and at the start of this year, there was scant evidence to suggest the team and its dominant driver Max Verstappen could be prevented from repeating its walkover.
But while it still has the fastest car in F1, Red Bull first slipped up in Australia due to reliability issues, and it was beaten again in Miami by Lando Norris, whose race pace in the upgraded McLaren was dubbed "insane" by Verstappen.
While Vasseur warned that Red Bull is "still ahead", he says the shrinking gap means Ferrari and McLaren will be able to put more and more pressure on the Milton Keynes-based squad, which can no longer cruise to race wins unopposed.
When asked by Motorsport.com if Miami is a taste of what's yet to come in 2024, Vassseur replied: "I think it's almost like this since the beginning of the season, depending on the track.
"Honestly, Red Bull is still ahead. Probably Max could have won today without the story of the safety car. They did the pole position, which means they have still a small advantage.
"What is true is that compared to one year ago, when we are able to do a good job and to put everything together, we are there. It means we are putting them a little bit under pressure, they have to be a bit more aggressive with the strategy.
"They are not anymore in the comfort zone of last year where it doesn't matter what happens and after lap two they were in front."
The smaller pace deficit has bigger implications on race strategy, as with two equally strong cars Ferrari and McLaren can start asking serious questions of Verstappen, especially on races where Sergio Perez is on the back foot and won't be able to give Verstappen strategic cover.
"I think it's a game-changer in the management of the race," said Vasseur.
"This is an opportunity for us because if we are doing another small step, that we will be really in a position to fight with them every single weekend."
Following on from McLaren's Miami updates, Ferrari is preparing its first major upgrade package for next week's race at Imola's Emilia Romagna Grand Prix.
Ferrari took to its Fiorano test track this week to give its new parts a first shakedown during a 200km filming day.
