Daniel Ricciardo was “much more optimistic outlook” after Red Bull completed its strongest day of pre-season Formula 1 testing yet in Bahrain.

The Australian said the world champion team was “not up to scratch” after another difficult day yesterday, but made a significant improvement on day two on Friday.

Ricciardo set Red Bull’s fastest time around the Sakhir circuit so far and almost doubled the amount of laps he completed, from 39 yesterday to 66 today.

The RB10 completed a 20-lap run in the closing stages of the session and set the third fastest time, less than two tenths of a second adrift of Sergio Perez’s benchmark for Force India.

“A big improvement everywhere over yesterday and a much more optimistic outlook now I think,” said Ricciardo.

“We still have a lot to learn, but we’re making progress and the past two days have been a big step in the right direction.”

McLaren’s Jenson Button, who wound up more than a second adrift of Ricciardo in the final times, was impressed by the Red Bull’s progress.

“They’re pretty quick,” said Button. “And he did 21 laps, that’s a good percentage of the race – 35-40 per cent.

“We always knew that when they got their problems sorted they would be competitive – you just have to look at the car.

“I’m sure they still have their issues, but you can never write off a four-time world championship-winning team. They’ll be competitive. It’s just whether it’s at the first race or three races in.”

AUTOSPORT Live coverage of the final pre-season F1 test will resume at 6am UK time on Saturday morning