Team boss Toto Wolff declared Mercedes had "one of their worst days" in racing on Sunday after Lewis Hamilton and George Russell finished fifth and seventh at the Bahrain Grand Prix.
The Austrian, who on Saturday said his team had to go back to the drawing board and re-design their car, was backed by seven-time champion Hamilton who said the former champions had slipped to become 'the fourth-fastest team.'
In a race dominated by the triumphant Red Bull team, who were first and second with double champion Max Verstappen and Sergio Perez, Fernando Alonso, 41, charged through to finish third on his debut with Aston Martin after outpacing Hamilton.
"They were just quicker than us," said a calm Hamilton. "The Ferraris are quicker than us. We're the fourth-fastest team."
Carlos Sainz finished fourth for Ferrari after team-mate Charles Leclerc's retirement with a power failure, while running third.
"That was one of our worst days in racing. It was not good at all," said a downcast Wolff, the man who had led Mercedes to eight consecutive constructors' championship titles from 2014 to 2021.
"We are lacking pace front, right, and centre. The Aston Martins are very fast and the Red Bull is just on a different planet.
"It hurts that they are so far ahead. It reminds me of our best years where we put one second on everyone else. That is the benchmark.
"We need to put one foot in front of the other to come back, but nobody in this team will throw in the towel.
"We need to dig deep, deeper than we ever have done before. And we can do that…"
The bleak outlook for Mercedes was made worse by the knowledge that, essentially, Aston Martin are a 'customer' team running a Mercedes engine, gearbox and transmission, but in a car designed independently.
With Hamilton, 38, in the final year of his contract after winning six of his seven drivers' titles at Mercedes, facing a dilemma over his own future, the once all-conquering 'silver arrows' have a potential crisis.
That Hamilton was passed by Alonso and Russell by Stroll, in the second Aston Martin, during the race served only to add to Mercedes' pain and stiffen Hamilton's resolve to push for a new concept with their car.
He suggested the team needed to persevere with the existing design – which was created for the new 'ground effect' era last year but flopped – while also planning a new one.
"We've just got to keep working," said Hamilton. "We know we're not where we need to be and we know that this isn't the right car.
"It's a difficult one, but I've just got to try and stay positive, keep my head up and keep pushing the guys, keep trying to be a positive light for them and get the best points I can on a weekend."
He added praise for the remarkable job done by Alonso and Aston Martin.
"He did a great job and it's really amazing to see. And to all the Aston Martin team, they did such an amazing job. So we've got work to do because half their car is ours and they do their aero in our wind tunnel. So, we've got some work to do…"