Finland's Kimi Raikkonen topped the times for Lotus in Friday afternoon's second free practice session for this weekend's Bahrain Grand Prix, just ahead of motivated Mark Webber and leaving Lewis Hamilton looking to make up ground.
Driving with typical aggression and aplomb, the 'Ice Man' clocked a best time of 1min 34.154sec on his medium tyres midway through the 90 minutes to outpace Webber of Red Bull by 0.03sec.
Webber, preparing for his 200th Formula One race on Sunday, clocked 1:34.184 to finish ahead of his third-placed team-mate, defending triple champion Sebastian Vettel by almost one-tenth of a second.
After the agony and angst of their early-season intra-team problems - triggered by the ruthless Vettel's decision to ignore team orders and snatch victory from Webber in Malaysia - the Australian demonstrated that he has no intention of doing anything other than racing to win.
To achieve that, however, he may have to overcome an expected strong challenge from in-form Ferrari.
Two-time champion and winner of last Sunday's Chinese Grand Prix Fernando Alonso was fourth for the 'scarlet scuderia' ahead of Paul di Resta of Force India, Felipe Massa - who had been quickest in the morning's opening session - and Romain Grosjean in the second Lotus.
Nico Rosberg was eighth for Mercedes ahead of fellow German Adrian Sutil in the second Force India car and Hamilton, in the second Mercedes.
Jenson Button, seeking to close the performance gap to the leaders in his improving McLaren, was unable to rise beyond 11th, a full 1.2sec slower than Raikkonen on another hot and testing day at the Sakhir circuit, 25 kilometres (15.5 miles) into the desert from Manama.
The track temperature was 38 degrees Celsius (100.4 degrees Fahrenheit) and the air temperature a relatively moderate 33 degrees on the circuit - slightly cooler and more comfortable conditions than the previous day.
Britain's 2008 world drivers' champion Hamilton comes into the race after delivering two podium finishes and a pole position so far this season.
But a perplexed Hamilton said he and his Mercedes team were in a race against time after finishing down the field.
"We're working as hard as we can and we just need to find some more time from somewhere," he said.
"I don't really know where we are losing it. They have changed the car this weekend, changed the settings for what they think the track needs but I'm not convinced it is the right way to go.
"I don't know if they are right or wrong but we were struggling for pace today... But I am sure we will find it."
Opposition groups demanding more political freedoms in the Gulf kingdom have announced plans to protest as practice got under way and after clashes between radical groups and police overnight.
But there was no evidence of unrest in and around the track.