Finnish driver Valterri Bottas gave his Williams team the top spot by being the fastest on the final day of testing at Circuit de Catalunya, Barcelona.

Bottas was unchallenged in the qualifying simulation where he managed 1:23.063 on Pirelli supersoft's, leaving the rest of the field almost half a second behind.

"It was a really good day and a great way to finish the test," Bottas said in an article on Formula 1's official site.

"One of the main points we have learnt is that the FW37 is very reliable. The car we are taking to Melbourne is very competitive and should make for an interesting start to the season."

Sebastian Vettel, proved Ferrari's strong capability by trailing the Williams car no less than one second slower. Both Williams and Ferrari are considered to be the challengers of last year's champions, the Mercedes Benz Silver Arrows this season.

The third fastest is Felipe Nasr of Sauber, also finishing no less than one second behind Bottas. The newcomer clocked in the most laps of the day at 159.

Unofficial test times appear below via Formula1.com.

1. Valterri Bottas, Williams, 1:23.063

2. Sebastian Vettel, Ferrari, 1:23.469

3. Felipe Nasr, Sauber, 1:24.023

4. Max Verstappen, Toro Rosso, 1:24.023

5. Daniel Ricciardo, Red Bull, 1:24.638

6. Sergio Perez, Force India, 1:25.113

7. Nico Rosberg, Mercedes, 1:25.186

8. Jenson Button, McLaren, 1:25.327

9. Pastor Maldonado, Lotus, 1:28.272

Maldonado caused red flags to be raised when his car hit the barriers on Turn 4. The team said the cause of the accident was a "systems issue."

"It was a shame to end the day early, but that was the only issue we've had like this during testing," Maldonado explained in a statement published on Formula1.com. 

"The car was not too badly damaged and I am fine, so we can look to the positive that we have a lot of information to take the car in the right direction."

Formula 1 opens the season at the Rolex Australian Grand Prix in Melbourne on Mar. 13.