The Championship leader had to pass fellow BMW driver Andy Priaulx mid-race and defend the position vigorously to take his third victory of the season.
He took the lead on lap five, having dispatched polesitter Augusto Farfus Jr a lap earlier. Muller had to drive round the outside of Priaulx on the run down to Les Combes. Priaulx took the inside line to defend the position, but Muller had used the tow through Eau Rouge to slingshot the Brit.
Priaulx then fought back and tried to repeat the manoeuvre back on Muller, but to no avail. The pair finished just 0.270 seconds apart at the flag.
"It was really perfect with my fourth position on the gird I thought I could do well," Muller said. "I had a little luck - all the fighting was behind me."
That battle was for third, eventually won by BMW's Jorg Muller, who beat Farfus Jr and Gabriele Tarquini to the position.
Jorg Muller took the position on the final corner after colliding with Farfus Jr at the La Source hairpin. The pair continued the run down to the finish line with their body panels locked together and smoke pouring from the back of Jorg Muller's car thanks to a puncture. Muller took the position by less than three hundredths of a second.
Jorg Muller said he only hit Farfus Jr because of a tap behind from Tarquini. He said: "I finished third. That's it. I got pushed from Tarquini and hit Farfus. I kept full throttle and that's why I finished third but this was not clean race and I do not like it."
German Michael Funke brought out the safety car after a dramatic roll on the opening lap. Funke was pushed wide into the barrier at Eau Rouge on the opening lap, which pitched the Ford Focus into a roll. Funke was unhurt, but the car looks unlikely to be repaired for today's second race.
CLASSIFIED: Pos Driver Make Time 1. Dirk Muller BMW 320i 22:58.706 2. Andy Priaulx BMW 320i + 0.270 3. Jorg Muller BMW 320i + 5.448 4. Augusto Farfus Jr. Alfa Romeo 156 + 5.470 5. Gabriele Tarquini Alfa Romeo 156 + 5.712 6. James Thompson Alfa Romeo 156 + 5.859 7. Antonio Garcia BMW 320i + 10.694 8. Fabrizio Giovanardi Alfa Romeo 156 + 11.297 9. Roberto Colciago Honda Accord Euro R + 11.495 10. Jason Plato SEAT Toledo Cupra + 11.566 11. Peter Terting SEAT Toledo Cupra + 11.965 12. Rickard Rydell SEAT Toledo Cupra + 14.273 13. Jordi Gene SEAT Toledo Cupra + 15.697 14. Tom Coronel Seat Toledo Cupra + 16.329 15. Alain Menu Chevrolet Lacetti + 18.058 16. Giuseppe Ciro BMW 320i + 23.145 17. Stefano D'aste BMW 320i + 23.655 18. Nicola Larini Chevrolet Lacetti + 24.208 19. Marc Hennerici BMW 320i + 26.567 20. Valle Makela Seat Toledo Cupra + 27.660 21. Adam Lacko BMW 320i + 29.982 22. Thomas Klenke Ford Focus + 30.119 23. Carl Rosenblad BMW 320i + 30.841 24. Soheil Ayari Peugeot 407 +1:06.782 NOT CLASSIFIED/RETIREMENTS: Driver Male On Lap Robert Huff Chevrolet Lacetti 4 Michael Funke Ford Focus 0
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