While the German was fastest in a dry second practice, Fernando Alonso ended the session just 17 thousandths of a second down the road.
The Spaniard had earlier led Felipe Massa home in a Ferrari one-two in mixed conditions in FP1.
Despite Ferrari having generally proved more competitive in race trim rather than over one lap this year, Vettel believes Red Bull is in good shape for Sunday's race at Barcelona.
"I think they have always been strong in the race, so we will see," Vettel said when asked about Ferrari's performance.
"We were pretty happy today trying to get as much information on both sets of tyres, both compounds, and we have to go from there.
"This morning was a waste of time in those conditions but this afternoon was fairly conclusive.
"It is better to be more or less on the top of the timesheet than somewhere in the middle on Friday.
"It is difficult to predict the weather on Sunday [though], so we have to wait, focus on the car now and have a good free practice tomorrow morning and hopefully a good qualifying to prepare for the race."
Vettel warned that Red Bull could not expect much assistance from Pirelli's experimental new hard tyre compound, saying it did little to arrest his team's previous concerns about aggressive compounds.
"It is difficult to say a lot about the new hard tyre: we didn't expect any miracle and as it turned out I don't think it is a massive difference," Vettel explained.
"I don't think it helps us in terms of changing the race completely so we will see a similar amount of pit stops as last races.
"We started going into the weekend knowing we have to stop many times, and judging by this afternoon there is no change.
"Right now it is difficult to predict how many times we have to stop, but in terms of pace we are there or thereabouts with the top guys."
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