Lewis Hamilton lapped six tenths of a second faster than Mercedes team-mate Nico Rosberg in a twice halted Belgian Grand Prix practice session on Friday.
After championship leader Rosberg had set the pace in the morning with a lap just 0.097 seconds faster than the Briton's best, Hamilton turned the tables after lunch with a substantially quicker effort.
The time of one minute 49.189 was 0.604 better than Rosberg's on a cloudy but bright day at the longest track on the calendar, where the weather can combine the seasons in the space of an afternoon.
Rosberg had topped the first session timesheets in 1:51.577 as the two title rivals – separated by just 11 points after 11 of 19 races – renewed their duel after the August break with their domination intact.
The afternoon running was interrupted when Venezuelan Pastor Maldonado crashed his Lotus into the barriers on the way to Pouhon.
There was a further stoppage in the first half hour when Mexican Esteban Gutierrez's Sauber spun and was stranded on the track at Blanchimont.
