Vettel's Ferrari team stood as the pre-season favourite after Barcelona testing, and Mercedes publicly acknowledged that the Italian outfit looked to have the edge.
Speaking after Friday running, Vettel jokingly referred to pre-season claims of Mercedes' struggles as “bullshit”, before adding that he was genuinely surprised by the German team's performance.
Vettel and new teammate Charles Leclerc were both within a tenth of Hamilton in FP1, but slumped to fifth and ninth respectively in the second session.
Asked why Ferrari lacked pace compared to Mercedes in FP2, Vettel said: “We don't know the reasons but we're looking for them.
The German said Ferrari “didn't get into the groove” on Friday, and believes there's a lot of laptime to be picked up once he regains confidence in the car.