Britain’s Lewis Hamilton set the pace in opening free practice for the Malaysian grand prix on Friday as Mercedes also showed blistering speed aided by their controversial new rear wing.

McLaren driver Hamilton, the 2008 world champion, set the quickest time of one minute 38.021 seconds in the 90-minute session, held in scorching heat at the Sepang circuit, half a second ahead of reigning titleholder Sebastian Vettel.

Mercedes’ Nico Rosberg and Michael Schumacher held the third and fourth positions, in a performance which will bring more attention to their new drag-reduction device despite its all-clear by Formula One officials.

Lotus driver Romain Grosjean placed fifth ahead of Vettel’s Australian Red Bull teammate Mark Webber, while McLaren’s Jenson Button, who won last week’s season-opener in Australia, was ninth.

Despite concerns from rival teams, officials have raised no objections to Mercedes’ “W-duct” rear wing which cleverly channels air-flow to cut resistance on the nose when the Drag Reduction System (DRS) overtaking aid is engaged.