Yvan Muller was fastest in Saturday morning's first World Touring Car Championship practice session at Sonoma.
After suffering turbo trouble in Friday's test, Tom Chilton produced a greatly improved performance in his Arena Ford to take second, just 0.053s off the world champion's 1m46.398s lap.
"On Friday we had a pipe come out on the turbo, so I was effectively driving a 1.6-litre atmospheric [rather than a turbo car]," said Chilton. "We looked at the data and were quite encouraged to see that the problem was costing us 1.5s."
Muller's Chevrolet team-mate Alain Menu was third fastest, ahead of the leading SEAT, that of Lukoil driver Gabriele Tarquini.
"I am really enjoying this circuit," said Tarquini. "For me, Macau is the most dangerous track on the calendar, but this circuit is really challenging and really nice."
Independent BMWs completed the top six. Hungaroring reversed-grid racewinner Norbert Michelisz's Zengo entry led Mehdi Bennani's similar Proteam machine.
The second Arena Focus of James Nash was seventh, just 0.040s ahead of Franz Engstler's BMW.
Engstler suffered a huge slide on his final timed lap, after the chequered flag had been shown, and lost his left wing mirror in light contact against Turn 8's concrete wall.
Several drivers joined Engstler in exploring the limits of adhesion. Salzburgring racewinner Stefano d'Aste brought a large amount of dust onto the circuit after an off at Turn 2.
Special Tuning's Darryl O'Young and Friday test pacesetter Alex MacDowall subsequently lost control at Turn 2, prompting officials to stop the session to allow for the circuit to be cleaned.
Others to encounter difficulties included Italian Superstars champion Alberto Cerqui, who escaped damage in a very wide off-track moment at the Carousel.
WTCC debutant Robb Holland only took to the track in the last five minutes, after the session had been restarted, and ended the morning in 20th.
Proteam has withdrawn Felice Tedeschi's BMW from this weekend's meeting, after the Italian debutant sustained heavy damage in a roll at Turn 4 during Friday's test.
Pos Driver Team/Car Time Gap 1. Yvan Muller Chevrolet 1m46.398s 2. Tom Chilton Arena Ford 1m46.451s + 0.053s 3. Alain Menu Chevrolet 1m46.574s + 0.176s 4. Gabriele Tarquini Lukoil SEAT 1m47.009s + 0.611s 5. Norbert Michelisz Zengo BMW 1m47.032s + 0.634s 6. Mehdi Bennani Proteam BMW 1m47.264s + 0.866s 7. James Nash Arena Ford 1m47.306s + 0.908s 8. Franz Engstler Engstler BMW 1m47.310s + 0.912s 9. Robert Huff Chevrolet 1m47.319s + 0.921s 10. Aleksei Dudukalo Lukoil SEAT 1m47.328s + 0.930s 11. Pepe Oriola Tuenti SEAT 1m47.450s + 1.052s 12. Stefano D'Aste Wiechers BMW 1m47.469s + 1.071s 13. Darryl O'Young Special Tuning SEAT 1m47.732s + 1.334s 14. Tom Boardman Special Tuning SEAT 1m47.743s + 1.345s 15. Fernando Monje SUNRED SEAT 1m47.769s + 1.371s 16. Alex MacDowall Bamboo Chevrolet 1m47.774s + 1.376s 17. Tiago Monteiro SUNRED SEAT 1m48.030s + 1.632s 18. Alberto Cerqui ROAL BMW 1m48.554s + 2.156s 19. Tom Coronel ROAL BMW 1m49.082s + 2.684s 20. Robb Holland Bamboo Chevrolet 1m50.193s + 3.732s 21. Charles Ng Engstler BMW 1m51.305s + 4.907s