Red Bull reckons that its Formula 1 title hopes now rest on engine partner Renault's rate of progress with its V6 turbocharged unit.
After a stronger-than-expected start to the campaign for Red Bull, early season pacesetter Mercedes fears that Red Bull is now back in the championship fight.
But Red Bull boss Christian Horner believes that the key factor that will define its campaign will be how much progress Renault can make.
"It is a big gap [to Mercedes]," he said. "They have plenty up their sleeves at the moment.
"I think we have done incredibly well to get as close to them as we did this weekend.
"Their advantage is clear. It is in a straight line and we are working hard with the guys from Viry [Renault's French base].
"Considering where we are at with our engine, to do what we are doing is beyond our expectation.
"Renault knows there is a lot more to come once they sort out driveability and so on.
"Hopefully our curve in terms of catching up with straightline speed, while it is steep, we should hopefully we able to make steps."
Although F1's new turbo engines have been homologated, Horner thinks that Renault is able to improve a lot because the hardware does not need tweaking.
"A lot of their issues are software related, and hopefully steps can be made and we can close that gap," he said.
"These engines are so complicated. But hopefully it is a matter of getting all three elements working in harmony, which is the combustion engine, the turbo and the energy recovery system.
"These all affect the braking as much as the acceleration and power delivery.
"It is a matter of making those three elements work in harmony and, at the moment, we are not there yet."
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