Ferrari's Charles Leclerc topped the morning timesheets on the final day of Formula One's preseason test in Bahrain on Saturday but said Red Bull remained the team to beat.
The Monegasque lapped the Sakhir circuit with a fastest time of 1:31.024 seconds on the Pirelli C4 tyres, 0.418 quicker than Mercedes' George Russell who was using the softer C5 rubber.
"I feel we've got some work to do," Leclerc told reporters after handing over to teammate Carlos Sainz for the final session. "Red Bull seems to be very strong in these three days."
Leclerc was runner-up last year to Red Bull's double world champion Max Verstappen, and the pair will be renewing their rivalry when the season starts in Bahrain next week.
The Ferrari driver said he felt in the best shape of his life after some extreme winter training in the Dolomites, and was fully recharged.
Ferrari started last year strongly, with Leclerc winning two of the first three races, before the challenge petered out in strategic errors, poor reliability and driver mistakes.
Mattia Binotto has left as principal since then, replaced by Frenchman Fred Vasseur whose task is to deliver the team's first championship since the constructors' title in 2008.
Leclerc said the new SF-23 car was a very different one to last year's.
"I've been trying a lot of different driving styles. I seem to have found my way a little bit this morning, finally," he said. "I expect us to be a bit quicker in the straights, maybe struggling a little bit more in the corners.
"We are still working quite a bit on trying to find the sweet spot of the car in terms of setup so I hope there's some margin on that still, that we haven't found the sweet spot yet."
Verstappen, who was quickest in both sessions on Thursday and second on Friday evening, told reporters he was happy with his car even if it remained a work in progress.
"It's been very good," he said. "I think the car's working really well. Just going through a lot of things we wanted to try and it's very interesting what we have been trying.
"Very positive days for me and just enjoying driving the car. Overall I think it's definitely an improvement to last year."
Red Bull won 17 of 22 races last year, with Verstappen triumphant in 15 of them.