The Italian squad is going in search of its first victory of the season, as it was this event 12 months ago where Vettel picked up his last win.
It was not a smooth session for Lewis Hamilton, who missed out on a lot of running following an issue with his throttle pedal, which occurred on the circuit.
The Briton was coasting through the middle sector before he found power once more to return to the pits, where he stayed for almost an hour.
However, he was able to get back out onto the circuit and end the session in sixth, behind teammate Valtteri Bottas and 1.3 seconds down on Vettel.
Just one-tenth split the duo, as the team looks to continue its strong run of momentum that it picked up towards the end of the first half of the season.
A virtual safety car was deployed while the debris was cleared up along the Kemmel Straight.
Bahrain International Circuit - Winter testing