The German steered the car he has nicknamed ‘Hungry Heidi’ around the Melbourne street circuit in one minute 25.908 seconds half an hour before the end of the second session.
That lap topped the time sheets for the day, edging his Australian team-mate Mark Webber (1.26.172) into second as the Red Bull team scattered a few seeds of doubt over the consensus that the gap to the rest of the grid was narrowing.
“Overall it was a good day for us, it was pretty seamless and there was no trouble with the car,” Vettel said. “After all the mileage of testing, it was fun to be out there – this circuit doesn’t get easier.”
Nico Rosberg (1.26.322) was the best of the rest on what would have been an encouraging day for Mercedes had he not later ground to a halt with a gearbox problem moments after team-mate Lewis Hamilton had driven over the gravel and into a wall.
Kimi Raikkonen, third in the championship last year, and Romain Grosjean grabbed the fourth and fifth best times to confirm some impressive pre-season showings for Lotus.
Fernando Alonso and Felipe Massa had more competitive first than second sessions for Ferrari, finishing sixth and eighth fastest overall to sandwich the luckless Hamilton.