The series' newly-crowned champion beat his Scandinavian counterpart by just over three tenths of a second, in the process setting the fastest time so far this weekend.
Bjork, who once again set his best time in the opening minutes, was able to hold onto second ahead of Chilton.
The Briton had led RML Chevrolet team-mate Muller out for the latter's flyer, and while the duo reversed roles in the final minutes neither was able to improve.
James Thompson continued his and Lada's strong start to the weekend by sealing fourth, just over half a second down the road from Muller.
Bamboo locked out fifth and sixth through Alex MacDowall and James Nash respectively, while Pepe Oriola just shaded Tiago Monteiro's Honda and Rob Huff's SEAT in the fight for seventh.
Gabriele Tarquini meanwhile stole into 10th at the flag, demoting a BMW trio of Stefano D'Aste, Tom Coronel and Franz Engstler in the process.
Engstler was the session's only spinner, losing his BMW at Turn 11, while Jeronimo Badaraco missed the second half of the session after coming to a halt on the outside of Turn 13.
Pos Driver Team/Car Time Gap 1. Yvan Muller RML Chevrolet 1m55.508s 2. Thed Bjork Polestar Volvo 1m55.848s +0.340s 3. Tom Chilton RML Chevrolet 1m55.910s +0.402s 4. James Thompson Lada 1m56.069s +0.561s 5. Alex MacDowall Bamboo Chevrolet 1m56.109s +0.601s 6. James Nash Bamboo Chevrolet 1m56.196s +0.688s 7. Pepe Oriola Tuenti Chevrolet 1m56.204s +0.696s 8. Tiago Monteiro Honda 1m56.261s +0.753s 9. Rob Huff Munnich SEAT 1m56.341s +0.833s 10. Gabriele Tarquini Honda 1m56.455s +0.947s 11. Stefano D'Aste PB BMW 1m56.479s +0.971s 12. Tom Coronel ROAL BMW 1m56.527s +1.019s 13. Franz Engstler Engstler BMW 1m56.574s +1.066s 14. Rene Munnich Munnich SEAT 1m56.708s +1.200s 15. Rickard Rydell Nika Chevrolet 1m56.847s +1.339s 16. Norbert Michelisz Zengo Honda 1m56.946s +1.438s 17. Tom Boardman Special Tuning SEAT 1m56.997s +1.489s 18. Hugo Valente Campos SEAT 1m57.017s +1.509s 19. Marc Basseng Munnich SEAT 1m57.036s +1.528s 20. Fernando Monje Campos SEAT 1m57.345s +1.837s 21. Freddy Barth Wiechers BMW 1m57.496s +1.988s 22. Darryl O'Young ROAL BMW 1m57.533s +2.025s 23. Charles Ng Engstler BMW 1m57.926s +2.418s 24. Mikhail Kozlovskiy Lada 1m57.950s +2.442s 25. Yukinori Taniguchi Wiechers BMW 1m58.616s +3.108s 26. Filipe de Souza China Dragon Chevrolet 1m59.732s +4.224s 27. Henry Ho Engstler BMW 2m00.586s +5.078s 28. Kin Veng Ng China Dragon Chevrolet 2m01.911s +6.403s 29. Ka Lok Mak RPM BMW 2m02.726s +7.218s 30. Jeronimo Badaraco Son Veng Chevrolet 2m02.774s +7.266s 31. Mehdi Bennani Proteam BMW -
Volvo gave the World Touring Car Championship a major boost when it announced it would enter the series, but its ambitions don't stop there. JACK COZENS examines its programme, the S60 and what its arrival means for the WTCC
The 2012 World Touring Car champion says he never had the money to race cars. Yet 2015 is his 11th season in the WTCC. He talks STUART CODLING through his journey from motorsport fan to paid professional - for little more than £100,000