McLaren has fired a warning shot across the bow of its main rival Red Bull by setting fastest times in both of today's practice sessions for the Turkish Grand Prix.
Lewis Hamilton led his team-mate by almost a full second in this morning's opening session, but the reigning champion fought back in the second runs to claim the top spot. He ended the session less than 0.1sec faster than Red Bull's Mark Webber, with Sebastian Vettel in third and Hamilton back in fourth.
Red Bull's surprise at being outpaced was swiftly replaced by concerns over reliability; Webber pulled his car off the track with wisps of smoke coming from its rear end, and Vettel had questioned his car's water pressure.
The race already looks like being a straight fight between McLaren and Red Bull; Fernando Alonso was 0.5sec off the pace in his Ferrari, and Robert Kubica, the surprise package at Monaco two weeks ago, finished this morning's sessions behind both Mercedes and almost a second shy of Button's time.