Montmelo, Spain - Williams and Ferrari are poised to make a good start to the Formula One season after both finished winter testing with another strong showing on Sunday.
Valtteri Bottas steered his Williams to the fastest time on the final of 12 days of preseason tests, with Ferrari's Sebastian Vettel right behind him at the Barcelona-Catalunya circuit.
Bottas clocked an early flying lap of 1 minute, 23.063 seconds. The Finnish driver and team-mate Felipe Massa have consistently been among the fastest performers with both in the top two times through the final four days of testing.
Vettel and Sauber's Felipe Nasr were both less than one second slower than Bottas. Nasr put in the most laps of the day with 159
in another promising ride by the newcomer.
CAN MERC BE BEATEN?
Whether a revamped Ferrari and confident Williams can challenge champion Mercedes is another issue.
Nico Rosberg may have had a subdued final turn behind his Mercedes, but the German team has given no indication of slippage after dominating last season when Rosberg was Lewis Hamilton's only challenger for the title.
The Mercedes pair had set the pace on the previous two days, with Rosberg recording the fastest overall lap time in eight days at Montmelo of 1 minute, 22.792 seconds.
Toro Rosso's precocious Max Verstappen, who at 17 is the youngest F1 driver in history, again proved steady behind the wheel with the fourth fastest time. He was followed by Red Bull's Daniel Ricciardo.
Next came Sergio Perez in his first turn behind Force India's new car, right in front of Rosberg.
McLaren's Jenson Button, meanwhile, toiled to another session-low 30 laps after only managing two before the lunch break.
McLaren has been in a mechanical muddle as it adjusts to its new Honda engines. It was also without driver Fernando Alonso for the final four days of testing while he recovers from a scary crash here last weekend.
McLaren only managed to complete 380 laps this preseason. Compare that to Mercedes at 1,274 laps. Or Force India, which in only two and a half days, still racked up 365.
Lotus' Pastor Maldonado was the day's slowest driver, and the only one to end up in the barrier when he went off course at curve four.
The Australian Grand Prix is in two weeks.
Sapa-AP