McLaren's Daniel Ricciardo led the second morning of Formula One testing in Bahrain on Saturday, while seven-times world champion Lewis Hamilton spun his Mercedes into the gravel and brought out red flags.
Double world champion Fernando Alonso, who has replaced Australian Ricciardo at the Renault team now renamed as Alpine, began his comeback after two years away with the second-quickest time.
Ricciardo was also the fastest in Friday's opening session at the Sakhir circuit.
Spaniard Alonso did 59 laps, seven more than Ricciardo, in his first appearance in the A521 and was 0.124 slower than the Australian's best effort of one minute 32.215 seconds on the medium tyres.
Mexican Sergio Perez, taking over from Max Verstappen in the new Red Bull, was third quickest.
Hamilton was only eighth, and 1.184 off the pace, but completed 58 laps after a difficult opening day for the champions.
Mercedes still lost precious time after a gearbox problem cost them most of Friday morning's running.
Hamilton slid backwards into the gravel at turn 13, just after the halfway point of the session and, wheels hopelessly spinning, forced a halt for some 15 minutes.
The car was transported back to the pitlane, shrouded in a black sheet, to be cleared of gravel before Hamilton returned for the final hour before lunch.
Other drivers, including Ferrari's Carlos Sainz, also went off or had spins in challenging conditions with the wind direction shifting.
Aston Martin's Sebastian Vettel sat out most of the session due to a gearbox issue and did only nine laps.
Teams have only three days of testing before the first race in Bahrain on March 28.