However, the pace of the Silver Arrows failed to come to light in the afternoon, as Valtteri Bottas in fourth place was over six-tenths down on Vettel, who clocked a 1:16.607.
Alexander Albon failed to set a competitive time during the session, as he crashed on the exit of Turn 7, losing the rear of the car as he turned into the corner.
The Thai-British driver clouted the wall and sustained major damage to his front right suspension, putting him out of the session.
Charles Leclerc also found himself facing the wrong way twice throughout the session, losing the rear of his car at Turn 1 before spinning right at the end of the 90 minutes at Turn 8.
Leclerc was third on the times for Ferrari, but was almost half a second down on teammate Vettel. Lewis Hamilton failed to recapture his morning pace, and was almost a full second down in fifth place.
However, Carlos Sainz, who was the quickest midfield driver after FP1, was less than a tenth behind Gasly in his McLaren.
Bahrain International Circuit - Winter testing