Jenson Button has joined the list of those billing Williams and Mercedes as this season's early favourites but warned against writing off Red Bull.
Williams left the final Bahrain test at the top of the timesheets with Felipe Massa setting the fastest time at the Sakhir circuit by 0.020s ahead of Lewis Hamilton.
His Williams team-mate Valtteri Bottas topped the table for the most laps completed ahead of Sergio Perez and Massa.
The Grove-based team's showing has led several to predict that along with Mercedes they will enter this year's Championship as the early favorites.
In an interview with Sky Sports News Button gave his opinion, saying: "It has been a messy winter for a lot of people in terms of mileage on circuit. The two that you would pick out that look strong and consistent are Mercedes and Williams.
"In a way it is not good when you are behind certain teams, but I am happy for Frank Williams that they have a competitive car so far this year. I think those are the two teams to beat right now.
"We didn't have our upgrade on the car in testing - we did actually have it on, but we didn't get to run it as we had a few issues - so for the moment we don't really know where we stand.
"Those two are the teams that I think looked strongest over winter testing, whether that will be the case when we get to Melbourne - it is a very different circuit to Bahrain - we have to wait and see."
Pressed as to whether his own McLaren team were fourth in the pecking order behind Ferrari, Button said: "I'm not really sure Ferrari are third quickest either.
"The Force India looks quick, the Red Bull when it is running is very quick, so I don't think we know at all.
"We tried to concentrate on ourselves during testing, but you can't help but look at lap times and consistency through runs because you can normally tell what fuel people are running.
"Bahrain is a unique circuit and the first couple of races on the calendar are very different types of circuit, so we might see some different results when we go to different kinds of circuits."
Asked about Red Bull's chances of bouncing back, Button refused to make any predictions other than to say that the start of the season would be the perfect time for F1's traditional backmarkers to take advantage of others' issues.
"I think you will see them putting in very good laps in qualifying. Whether they can get to the end of a race or not I don't know," he said.
"For any team, to get to the end of a race is very difficult - especially at the start of the season - and if you do get to the end of the race there are some good points up for grabs.
"I think for the smaller teams it is the best chance to score points - especially the two teams that haven't scored a point in F1.
"It is going to be a tough start to the season, reliability is important, but to win you just don't need reliability, you need a competitive car and an intelligent team behind you that really understands what it takes to win a race."
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