Mercedes have lorded over Formula One for the last three years as the dominant team but Sebastian Vettel's accomplished victory for Ferrari in Australia Sunday has the reigning champions bracing for a season-long battle.
Vettel held all the aces in the Melbourne season opener mastering Lewis Hamilton by almost 10 seconds and his Mercedes team-mate Valtteri Bottas.
While only the first of a 20-race season, Vettel's showing for Ferrari has signalled a possible changing of the guard in the new era of faster and more physical cars.
"We've got a real race on our hands and it's a challenge we will relish. It's going to be great for the fans," declared Hamilton after he failed to make any impression on Vettel's tearaway Ferrari in the closing stages of the 58-lap dash around the Albert Park street circuit.
Mercedes executive director Toto Wolff, who only this week hailed Hamilton as in a "league of his own", admitted there was now a "more stressful season" ahead for his team on the evidence of the opening race.
"We saw that Ferrari were very strong in testing and in qualifying they were a real force," Wolff said.
"It's going to be a more stressful season than in the past but it's personality building."
Hamilton, although claiming his fourth successive pole position for the Australian race, had warned during the lead-up of the dangers Ferrari posed.
"I don't lie and I'm not very good at bluffing," Hamilton said.
"I didn't know how quick they would be in the race but their pace from testing was true and their first stint on the ultrasoft tyres was fantastic.
"My real strength wasn't until right at the end by which time it was far too late.
"I only stopped a lap earlier than my target but I couldn't go any further. We've got a race on our hands.
"It's always been tough to follow and for me it was as tough as I anticipated.
"For me personally, I want more wheel-to-wheel racing and it's currently through pit stops that we're fighting. We need to try and make sure we stay out front."
Finland's Bottas, who grabbed a podium place in his first race for Mercedes, said: "It is going to be a big challenge from Ferrari."
After the Australian opener a rare sight in the constructors standings with Ferrari on top with 35 points leading Mercedes by four points.