For the first time in a couple of years, Mercedes are genuinely wary of a Formula One rival.
While Mercedes drivers Nico Rosberg and Lewis Hamilton finished one-two in Sunday's Australian Grand Prix, they were looking in their rearview mirrors at Ferrari's Sebastian Vettel.
Ferrari's lead driver came third, butthe result could have been different if not for his team's tyre choice - they went soft, while Mercedes went harder in a decisive factor in the race.
"We went for the aggressive route," Vettel said.
"Maybe with hindsight we could have done something else, but I'm not willing to blame anything or anyone."
Mercedes' triumphant Rosberg described the choice of tyres as pivotal in the Albert Park result.
"The strategy was crucial," he said.
And his teammate Hamilton noted the improvements in Ferrari compared to last season when Mercedes blitzed the field.
"Ferrari's are obviously in the battle," Hamilton said.
"So hopefully some exciting races coming up ahead of us."
Australian Daniel Ricciardo is also eyeing further improvement in his Red Bull Racing car after finishing an encouraging fourth in Melbourne.
"It's a better result than we expected," he said.
"I'm happy with that, but, more than anything, I'm happy with the pace we had.
"We were still not as quick as Ferrari or Mercedes, but at parts of the race we weren't really far off."
