Vettel led a Red Bull one-two, setting a benchmark time of 1 minute 44.249, over half a second clear of teammate Mark Webber.
Mercedes were Red Bull’s closest challengers with Nico Rosberg setting the third quickest time, a whole second off the pace, followed by teammate Lewis Hamilton — who topped the first session — as the Silver Arrows showed improved form on the high-downforce track after a slight dip in Belgium
Ferrari — who seemed to have recovered from their mid-season slump and were Red Bull’s closest challengers around Spa and Monza — appear to have fallen back again with Fernando Alonso only managing sixth, the Spaniard’s title hopes looking increasingly bleak. The Maranello-based squad were testing a number of upgrades over the two one-and-a-half-hour practice sessions but both Alonso and teammate Felipe Massa seemed to have to wrestle the car around the 5.065 kilometre circuit, the F138 looking unstable and uncomfortable to drive on the bumpy surface.
Behind Alonso, McLaren’s Jenson Button ended the session seventh, ahead of Kimi Raikkonen in the Lotus. Adrian Sutil in the Force India and Button’s teammate Sergio Perez rounded out the top ten.
Vettel heads into the Singapore race, round 13 of 19 with one hand already on the World Championship crown.
Photos: Salman Khan returns from Jodhpur to Mumbai
Pics: Sidharth Shukla-Rashami Desai's sizzling chemistry at TV show launch
Ooh La Lana! WWE Diva flaunts sexy curves in these 30 pictures
15 'peach' perfect photos of Priyanka Chopra at People's Choice Awards 2017
62 going on 16: These photos of Rekha prove she is 'forever young'