Ferrari is emerging from crisis and turmoil to become perhaps Mercedes' biggest threat for the 2015 title.
The beleaguered Italian team has been playing down its prospects amid sweeping personnel changes, but newcomer Sebastian Vettel and the SF15-T car hit the Jerez test track with immediate pace this week.
Continuing Ferrari driver Kimi Raikkonen got his first turn at the wheel on Tuesday and declared it a "completely different story" compared to 2014.
He said the revolution behind closed doors at Maranello was clearly "for the right reasons".
"You usually know if a car is good or not, and this year is a completely different story than last year as I had a good feeling straight away when I went out," said the normally reticent Finn.
Indeed, the red-coloured team is turning heads up and down pitlane.
"We are keeping an eye on the opposition," said Mercedes' Nico Rosberg, "especially Ferrari has been an eye-opener in the last couple of days.
"It will be an interesting year for Formula One," he predicted.
"Ferrari looks good for now," said the Australian.
Mercedes' team chairman Niki Lauda also admitted Ferrari's apparent return to form is a "surprise".
He told the Swiss newspaper Blick: "I deliberately put on my red sweater on Tuesday to motivate our guys. Ferrari should be our main opponents in 2015."
Pirelli chief Paul Hembery, however, is not so sure.
"If anyone wants to place a bet now, they should wait a bit longer," he is quoted by Brazil's O Estado de S.Paulo.
"It's still early. The Ferrari looks good, but I still see Mercedes as the favourite, based on what they did in 2014."