Vettel headed a Red Bull one-two in the second practice, with teammate Mark Webber a tenth of a second behind. Ferrari's Fernando Alonso — Vettel's title rival, just six points behind — was third fastest, six-tenths off the pace.
"The track improvement was quite big today, it was dusty to start and improved lap by lap, so I wouldn't be surprised if tomorrow the order is different, but we've had worse Fridays, so I am happy," Vettel said.
Alonso was banking on the evolution of the track over the race weekend to perhaps bring Ferrari up to Red Bull's speed.
Mercedes' Nico Rosberg was fourth and Lotus' Kimi Raikkonen was fifth ahead of the McLarens of Lewis Hamilton and Jenson Button.