33.852secs in the afternoon session, 0.168 quicker than team-mate Mark Webber, in hot conditions. Nico Rosberg clocked 1:34.114 for third.
Ferrari's Fernando Alonso, a distant second in the standings and hoping to put Vettel's celebrations on ice, was sixth fastest in the morning and only 10th in the second run, again unhappy about degrading tyres.
Sergio Perez, who suffered a hair-rising puncture at last weekend's South Korea race, skidded into a wall at high speed at the sharp "Spoon" curve, leaving his McLaren badly dented and needing to ice down his right wrist after returning to the garage.
Alonso, one of many drivers who blasted tyre-makers Pirelli after Korea, spun at the tricky ninth turn, trashing his compound rubbers in the process.
Asked about the state of his replacement hard tyres over the team radio, the Spaniard barked: "Zero!"
Kimi Raikkonen lasted just two minutes on his medium tyre run, forced to abandon his Lotus after burying it deep in the gravel, but still posted the fourth-quickest time of the second practice.
Vettel, who can become only the third man to capture four world titles in a row if he wins and Alonso finishes below eighth on Sunday, then overtook his rival to get him even hotter under the collar with track temperatures nudging above 40C (104F).
Vettel has won the last four grands prix to open a 77-point lead with only 125 available from the last five races.
Lewis Hamilton had lapped quickest in the day's first free practice in 1:34.157, three tenths clear of Mercedes team-mate Rosberg, in another lively session which included the worrying sight of a wheel hurtling through the air.
Marussia's Jules Bianchi hit a wall heavily at turn nine, ruling him out of P2 due to chassis damage, before Pastor Maldonado's Williams lost a wheel coming through Spoon.
"I lost a wheel," the Venezuelan coolly radioed his pit crew, the bouncing projectile well snaffled by marshals.
Maldonado's day came to a quick halt when, 12 minutes into the second run, he smashed into into the same wall that did for Bianchi.
A voice over the radio crackled to Maldonado: "Pastor, everything okay with the car? Oh!"