Vettel, who leads the drivers' standings by 90 points with just 100 left to play for over the final four rounds, was fastest in Friday morning's opening practice and improved further in the 90-minute afternoon session, lowering the benchmark to one minute 25.722 seconds, serving notice of his intention to wrap up a fourth successive world title
The 26-year-old went to top of timesheets early in the session but then received a radio message confirming his KERS power-boost system was not working. A quick-fix later and Vettel was back on track, taking his time into 1min 25secs territory for the first time.
Vettel's place at the top of the order in both sessions was not unexpected at a track he has made his own since its first appearance on the F1 calendar in 2011. He has won both races in India so far - leading all 120 laps across the two races. The German is also on a five-race winning streak and gunning for his 10th win overall this season.
Regardless of whether Vettel maintains his winning streak, the primary objective this weekend is to wrap up world title number four, which would make him only the fourth man to reach that milestone after Juan Manuel Fangio, Alain Prost and Michael Schumacher.
As in the morning's opening practice session, Vettel's team-mate Mark Webber was next up to secure another Red Bull one-two, the gap between the two men growing from just under two-tenths to a shade under three.
The in-form Romain Grosjean was third for Lotus, half a second clear of team-mate Kimi Raikkonen who, despite an early spin, improved significantly on his efforts in first practice when he finished a distant 17th.
Lewis Hamilton was seven-tenths off the pace in fourth place, with his Mercedes team-mate Nico Rosberg sixth.
Ferrari's Fernando Alonso - the only man who can still deny Vettel the title - was in fifth place after recovering well from a gearbox problem that saw him complete just six laps in opening practice.
Elsewhere, Williams' Pastor Maldonado had a busy day, enlivening a largely pedestrian first session with a spin and then having a wheel nut work loose from his right-front tyre in the afternoon, forcing him to park up.
McLaren's Jenson Button was 10th with Paul Di Resta 15th for Force India, while Marussia's Max Chilton once against propped up the pack.
Friday's practice sessions were preceded by the news that the legal threat to this weekend's race was at an end after a Supreme Court hearing into alleged tax irregularities was delayed until next week.
A petition seeking the cancellation of the race was lodged with India's Supreme Court earlier this week amid allegations that race organisers Jaypee Sports International Limited did not pay entertainment taxes due on last year's event.
However, a spokesman for the race organisers confirmed to Press Association Sport the hearing will now take place following Sunday's race, clearing the way for the 16th round of the season to go ahead as planned.