Williams again showed the F1 field the way in free practice as preparations geared up for qualifying at the British Grand Prix, with Nico Rosberg just getting the better of team-mate Kazuki Nakajima late in the hour.
The Japanese driver had pushed the Grove team to the front with seconds to go, but Rosberg saved his best for last, crossing the line after the chequered flag had fallen to beat his team-mate's 1min 19.102secs with a lap of 1min 18.899secs, becoming the only man to break through the 1min 19secs barrier so far this weekend.
Having each taken turns to lead the way, Jarno Trulli and Sebastian Vettel wound up third and fourth overall, just ahead of the Ferraris of Felipe Massa and Kimi Raikkonen, hinting that the battle for pole might be more open than Friday's earlier sessions had suggested.
Timo Glock, Fernando Alonso, Mark Webber and Rubens Barrichello rounded out the top ten in a session that started with the track still showing the odd damp patch and conditions cooler than of late, but passed off without incident. Points leader Jenson Button was twelfth, one spot behind countryman - and rival for the home nation's affections - Lewis Hamilton, while the bottom three was occupied by the two BMW Saubers, with Nick Heidfeld and Robert Kubica sandwiching Sebastien Buemi.