Red Bull’s Sebastian Vettel again left his competitors for dust as he set a blistering time in the Singapore Grand Prix’s final free practice session on Saturday.

The three-time defending world champion, who is threatening to turn the rest of this season into a parade, timed 1min 44.173sec as the sun set over the Marina Bay street circuit.

Vettel, also quickest in the second practice session on Friday, was 0.191 sec ahead of Lotus’s Romain Grosjean, with Mercedes’s Nico Rosberg third and Red Bull’s Australian driver Mark Webber fourth.

Lewis Hamilton was fifth for Mercedes with Ferrari’s Fernando Alonso, second in the standings but struggling to keep up with Vettel, sixth.

Paul Di Resta span into reverse early in the session and Esteban Gutierrez fought to hold on to a big lock-up heading into the sharp right-hander at turn 14.

Daniel Ricciardo, headed from Toro Rosso to table-topping Red Bull in the close season, struggled with brake problems and also locked up in the first half-hour.

Hamilton went streaking to the top of the time charts as the fast laps started around the half-hour mark, but the 2008 world champion was soon overhauled by the retirement-bound Webber.

Grosjean leapt to the front of the pack as teams switched to the faster, super-soft tyres in the final minutes, timing 144:364 in his Lotus.

But the session-leading time was quickly erased by the thunderous lap from Vettel, who has won the last two Singapore races and was also victorious in the previous two grands prix this season.

The young German, with a 53-point lead in the standings and a fourth world title in his sights, will be gunning for his fifth pole position of the year in qualifying from 8:00 pm (2200 AEST).