Max Verstappen topped the timing sheets as teams struggled with high track temperatures and gusting winds at the Sakhir circuit.
Lewis Hamilton’s fastest lap was just 0.110 seconds slower than the Red Bull driver but conditions are expected to favour Mercedes more when qualifying gets underway (4pm) with the sun setting.
But temperatures upwards of 35 degrees Celsius are still expected and the British driver admitted that qualifying and the race will be a battle inside the cockpit as much as anything else.
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“Racing in very hot temperatures takes its strain physically and even more mentally,” Hamilton said.
“As with all races, it's about maintaining absolute composure even when the conditions can be against you.
Lewis Hamilton believes the heat will cause him problems at the Bahrain Grand Prix
“We’re looking forward to the challenge and are focused on the task ahead.”
Hamilton is tied at the top of the F1 World Drivers’ Championship with Sebastian Vettel, who took the first Grand Prix of the season in Australia.
But the Brit, after finishing second in Melbourne, hit back with a win in China to level things up in the standings.
And he expects the ding-dong battle with the four-time world champion to continue for a good while longer.
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The Bahrain Grand Prix is set in the desert but the night race should allay temperatures
Ferrari will be Lewis Hamilton's likely closest challengers
“In race trim, Ferrari seem a couple of tenths quicker, so I'm expecting a great battle [in qualifying] and then again on Sunday,” Hamilton added.
“We'll work as hard as we can to try to close that gap."