SPA-FRANCORCHAMPS, Belgium - Red Bull's world champion Sebastian Vettel led Ferrari's Fernando Alonso at the top of the time sheets in final practice for the 2013 Belgian Grand Prix.Vettel lapped the 7km circuit, the longest and second fastest on the 2013 calendar, with a best time of 1min48.327 set in the last two minutes of the dry session on the medium tyre.Alonso had been quickest until then with a time 0.105 slower.ALONSO, VETTEL IN CHARGE AT SPAAlonso and Vettel, the 2013 Championship leader, were quickest during the first and second practice sessions respectively.They were also at the centre of a flurry of concern about the Pirelli tyres when both suffered right rear punctures within seconds of each other during second practice.After a full investigation, Pirelli ruled out any tyre-related issues and placed the blame on a metal plate shed from another car and found on the track during a later inspection.There were no visible tyre problems in during third practice session.Mark Webber, Vettel's team mate, was third fastest as he limbered up for what will be his last Belgian Grand Prix before moving to sportscar racing with Porsche at the end 2013.MERCEDES STRUGGLESToro Rosso's Jean-Eric Vergne was fourth with Ferrari's Felipe Massa fifth. McLaren's Jenson Button, 2012 race winner from pole, was an encouraging sixth on the timesheets.Mercedes appeared to be struggling, however, with Lewis Hamilton, who will be chasing his fourth successive pole later, only 12th fastest with team mate Nico Rosberg ninth.The timings meant Hamilton, the 2008 world champion and winner of the previous race in Hungary, had failed to appear in the top 10 in any of the three practice sessions.Vettel leads Kimi Raikkonen by 38 points with nine of the 19 races remaining. Alonso is a point behind Raikkonen and Hamilton a further nine adrift. 2013 Belgian Grand Prix at de Spa-Francorchamps:Final practice results1 Sebastian Vettel (Germany) Red Bull 1min48.327 2 Fernando Alonso (Spain) Ferrari 1min48.432 3 Mark Webber (Australia) Red Bull 1min48.5334 Jean-Eric Vergne (France) Toro Rosso 1min48.776 5 Felipe Massa (Brazil) Ferrari 1min48.788 6 Jenson Button (Britain) McLaren 1min48.882 7 Esteban Gutierrez (Mexico) Sauber 1min48.930 8 Romain Grosjean (France) Lotus 1min48.967 9 Nico Rosberg (Germany) Mercedes 1min48.993 10. Kimi Raikkonen (Finland) Lotus 1min49.008 11. Daniel Ricciardo (Australia) Toro Rosso 1min49.035 12. Lewis Hamilton (Britain) Mercedes 1min49.046 13. Adrian Sutil (Germany) Force India 1min49.122 14. Valtteri Bottas (Finland) Williams 1min49.177 15. Paul Di Resta (Britain) Force India 1min49.226 16. Sergio Perez (Mexico) McLaren 1min49.417 17 Nico Huelkenberg (Germany) Sauber 1min49.478 18. Pastor Maldonado (Venezuela) Williams 1min50.418 19 Charles Pic (France) Caterham 1min51.416 20. Giedo van der Garde (Netherlands) Caterham 1min51.800 21 Jules Bianchi (France) Marussia 1min52.221 22 Max Chilton (Britain) Marussia 1min53.507Second practiceFirst practiceStay with Wheels24 for the 2013 Belgian GP weekend.