Williams thinks it can beat Ferrari and be second to Mercedes in F1

The Grove-based outfit focused on reliability during the first week of testing and has shifted emphasis to performance during the last few days without going for headline times.

When asked for his read on where Williams stands in the pecking order, chief test engineer Rod Nelson said: "It's very close and every day's a little different.

"There's no doubt that Mercedes are extremely strong. Ferrari less so.

"We'd like to think we're slugging it out with Ferrari.

"We've got some more bits to bring to the car and I'm sure they have as well.

"Operationally we have to be as efficient as we can be.

"We'll do the best job we can. Merc's gone but we'd like to be second."

Nelson was pleased with the progress Williams has made in the last couple of days as it began stretching the limits of the car with qualifying simulations.

"The last couple of days in particular have been very good for us," he said.

"We spent most of last week looking at reliability stuff and doing our homework, and now we've started stretching the car a little bit more.

"We are still doing some longer runs looking at race pace and with a push towards qualifying - we're doing a one-hour quali session every day.

"We're not after headline times - we're doing the [qualifying simulation] session in the afternoon when it's generally slower because we want the best test conditions in the morning."