The Frenchman, who enters the weekend on the brink of a fourth WTCC crown, pulled clear with a 54.076s that proved comfortably faster than the rest of the field.
He had almost not started the lap however, coming close to hitting team-mate Tom Chilton on the lap immediately before he hit the front. The pair were collectively jockeying for clean air on the short 1.3-mile track.
Behind Muller it was far more congested, with just over four tenths of a second covering Alex MacDowall in second and Takuya Izawa in 16th.
Norbert Michelisz, Gabriele Tarquini, Fernando Monje, Rob Huff, Marc Basseng and Tom Chilton rounded out the top eight, all getting within 0.1s of MacDowall.
Morning pacesetter Tiago Monteiro was ninth, fractions ahead of Charles Ng - the Hong Kong driver having held top spot from the opening minute to the halfway mark, when he was demoted by MacDowall.
James Nash and James Thompson squeezed into 11th and 12th respectively, meaning Tom Boardman, Pepe Oriola and Tom Coronel were among those outside the theoretical Q2 cut.
Once again there was an almost continual stream of off-track incidents, although all were recovered without the need for red flags.
Basseng and Oriola both had quick laps ruined by off-track moments, while Muller, Monteiro, Chilton and Coronel were among those who ran wide at least once during the 30 minutes.
Izawa was once again fastest of the nine newcomers in 16th. Wiechers' Yukinori Taniguchi was next best in 19th, half a second down on his compatriot.
Pos Driver Team/Car Time Gap 1. Yvan Muller RML Chevrolet 54.076s 2. Alex MacDowall Bamboo Chevrolet 54.279s +0.203s 3. Norbert Michelisz Zengo Honda 54.303s +0.227s 4. Gabriele Tarquini Honda 54.309s +0.233s 5. Fernando Monje Campos SEAT 54.312s +0.236s 6. Rob Huff Munnich SEAT 54.323s +0.247s 7. Marc Basseng Munnich SEAT 54.324s +0.248s 8. Tom Chilton RML Chevrolet 54.340s +0.264s 9. Tiago Monteiro Honda 54.390s +0.314s 10. Charles Ng Engstler BMW 54.395s +0.319s 11. James Nash Bamboo Chevrolet 54.408s +0.332s 12. James Thompson Lada 54.439s +0.363s 13. Tom Boardman Special Tuning SEAT 54.519s +0.443s 14. Darryl O'Young ROAL BMW 54.612s +0.536s 15. Pepe Oriola Tuenti Chevrolet 54.713s +0.637s 16. Takuya Izawa Honda 54.749s +0.673s 17. Tom Coronel ROAL BMW 54.875s +0.799s 18. Mehdi Bennani Proteam BMW 55.079s +1.003s 19. Yukinori Taniguchi Wiechers BMW 55.192s +1.116s 20. Stefano D'Aste PB BMW 55.266s +1.190s 21. Hiroki Yoshimoto Nika Chevrolet 55.270s +1.194s 22. Rene Munnich Munnich SEAT 55.387s +1.311s 23. Masaki Kano Engstler BMW 55.555s +1.479s 24. Mikhail Kozlovskiy Lada 55.742s +1.666s 25. Jeronimo Badaraco Son Veng Chevrolet 56.371s +2.295s 26. Filipe de Souza China Dragon Chevrolet 56.573s +2.497s 27. Henry Ho Engstler BMW 56.673s +2.597s 28. Kin Veng Ng China Dragon Chevrolet 56.910s +2.834s 29. Ka Lok Mak RPM BMW 57.524s +3.448s
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