Mexico's Sergio Perez took his Force India to top place in pre-season testing at Bahrain's Sakhir circuit on Thursday while world champion Red Bull's winter woes continued.
As the final four-day testing period got underway, Perez clocked a best time of 1min 35.290sec with Valtteri Bottas continuing the early promise of Williams with the second-best time.
Kimi Raikkonen in a Ferrari, Mercedes' Nico Rosberg, Adrian Sutil in a Sauber and promising McLaren driver Kevin Magnussen filled out the top six.
"We really needed a good day to start this week and today we had it," said Perez after completing a marathon 105 laps.
"We managed to do a lot of laps, try several different compounds and mappings, and it's been a fantastic day in terms of learning about the car."