Nash, starting on reverse-grid pole, had initially lost out to Norbert Michelisz's Zengo Honda on the run down to the first corner, but fought his way back immediately to regain the lead by the end of the first lap.
The duo held position until the penultimate lap, when Michelisz was demoted by a charging Muller, who had started from 10th.
Just one second separated Nash and Muller heading into the final lap, but rather than come under pressure he was able to extend that advantage slightly en route to his first win in the series.
Muller claimed the second step of the podium, having claimed the scalps of Rob Huff, Gabriele Tarquini, Michel Nykjaer, Pepe Oriola and finally Michelisz during the 12-lap contest.
Tiago Monteiro held on to claim fourth despite late pressure from race one winner Nykjaer, who was in turn having to fend off the advances of Nash's Bamboo team-mate Alex MacDowall in the closing stages.
Behind them Oriola finished as top SEAT in seventh, with defending champion Huff unable to find a way past the second works Honda of Tarquini.
Tom Coronel also attached himself to the battle for eighth, although he was likewise unable to make a move stick on Huff.
Tom Chilton meanwhile was a casualty of a clash as the field ran through the Turn 1 chicane for the first time.
MacDowall and Lada's James Thompson were also caught out, but were both able to continue, with Thompson coming home 12th, just behind Marc Basseng in the second Munnich-run SEAT.
Results - 12 laps: Pos Driver Team/Car Time/Gap 1. James Nash Bamboo Chevrolet 17m36.853s 2. Yvan Muller RML Chevrolet + 1.438s 3. Norbert Michelisz Zengo Honda + 1.818s 4. Tiago Monteiro Honda + 3.483s 5. Michel Nykjaer Nika Chevrolet + 4.064s 6. Alex MacDowall Bamboo Chevrolet + 4.574s 7. Pepe Oriola Tuenti SEAT + 7.898s 8. Gabriele Tarquini Honda + 9.025s 9. Rob Huff Munnich SEAT + 9.483s 10. Tom Coronel ROAL BMW + 9.859s 11. Marc Basseng Munnich SEAT + 13.627s 12. James Thompson Lada + 14.145s 13. Fredy Barth Wiechers BMW + 14.556s 14. Franz Engstler Engstler BMW + 14.857s 15. Mikhail Kozlovskiy Lada + 15.155s 16. Mehdi Bennani Proteam BMW + 16.223s 17. Fernando Monje Campos SEAT + 27.497s 18. Rene Munnich Munnich SEAT + 41.749s 19. Charles Ng Engstler BMW + 46.282s Retirements: Tom Chilton RML Chevrolet 6 laps
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