Mark Webber kept Red Bull on course for a 14th pole position in as many races this season, when he lapped fastest in final free practice for the Singapore Grand Prix on Saturday.
The Australian lapped the floodlit 5.073-km Marina Bay Circuit in one minute 46.081 seconds on a dry night in the southeast Asian city-state.
McLaren's Jenson Button, who endured a miserable two sessions on Friday, split the Red Bulls with a fastest lap just 0.027 seconds slower.
German Sebastian Vettel, who can become Formule One's youngest double world champion this weekend with five rounds still remaining, was third fastest in 1:46.345, a day after he comfortably topped the timesheets in his Red Bull.
Vettel has converted 10 pole positions into eight wins this season and will again be a favourite in Saturday's qualifying session.
The 24-year-old was almost a second quicker than the field for a majority of the 60-minute session when soft tires were used. The cars looked better matched when they switched to the super-softs.
Two-time Singapore winner Fernando Alonso was fourth-quickest in his Ferrari, while McLaren's Lewis Hamilton was the only other driver to dip below 1:47 to round out the top five places.
The Mercedes pair of Nico Rosberg and Michael Schumacher finished sixth and seventh respectively, separated by just 0.006 seconds but well clear of Felipe Massa in the other Ferrari.
Vettel's soft tires lasted 16 laps in practice on Friday with almost no degradation and suppliers Pirelli expect a majority of the teams to adopt a three-stop strategy for Sunday's race.