Vettel, who has the chance to wrap up his fourth world title this weekend, bettered his timing of 1:26.683s set in the morning by clocking a new lap record of 1:25.722s in the second practice session at the Buddh International Circuit.
The German, who won the 2011 and 2012 Indian GPs, piped his teammate Mark Webber (1:26.011) by 0.289 seconds. Vettel was fastest in every practice session in India last year.
Only seven-time champion Michael Schumacher and the late Argentine Juan Manuel Fangio have won four successive titles since the championship started in 1950. Alain Prost of France is the sport's only other four-time champion.
In-form Romain Grosjean of Lotus (1.26:220s), who finished fourth in the morning, pushed hard in the intense second practice session but the two Red Bull cars were strong enough to come out on top in the end.
Mercedes' Lewis Hamilton (1:26.339s) too improved his FP1 timing to emerge as the fourth fastest.
Alonso did not have the best of the starts to his preparations as his run in the first practice session lasted just six laps because of gearbox problem. He was 12th fastest in FP1.
