F1: Bottas leads final Spa practice

Valtteri Bottas went quickest for Williams in a frenzied final few minutes of third practice for Formula 1's 2014 Belgian Grand Prix, outpacing Red Bull's Daniel Ricciardo by 0.268 seconds.

Mercedes driver Nico Rosberg was the best of the title contenders in third.

Many drivers only had the opportunity to run one or two flying laps on the soft Pirelli tyre at the end of the session, and were thwarted by traffic.

After overnight rain a dry line had already formed in some places, thanks to the preceding GP3 qualifying session, as the F1 cars took to the circuit for their installation laps.

With the surface still mostly wet, there was little activity for the first 30 minutes as most teams apart from the tail-enders elected not to risk their machinery.

Thus Marussia annexed the top two positions for half the session as Jules Bianchi (2m01.823s), Max Chilton (2m05.120s) and Andre Lotterer (2m07.529s) each essayed a tentative lap before reporting back to the pits.

Esteban Gutierrez was the first driver out on slick tires, half an hour into the session. He instantly took 1.581s out of Bianchi's time, then improved again by over four seconds as his medium-compound Pirellis came up to temperature, and this provided the cue for others to join the fray.

The track evolved quickly over the final 20 minutes as increased activity broadened the dry line, and Ferrari fans will have been heartened by the sight of Kimi Raikkonen bolting on a set of soft tyres and briefly topping the timesheets with five minutes to go.

Bottas, Ricciardo and Rosberg then went faster using the same tyre choice, but Lewis Hamilton and Fernando Alonso were unable to eclipse their team-mates and finished fifth and sixth fastest.

Sebastian Vettel finished the session outside the top 10 having done all his running on the medium compound.

He has reverted to an older engine after an ignition problem in one cylinder set in motion a failure of his nominated power unit on Friday.