Tackling low-grip track conditions in FP1, the reigning WTCC champion set a fastest time of 1m39.898s, before improving to a 1m39.505s in the second session.
Honda's Gabriele Tarquini was Muller's closest competitor in both sessions, and the Italian believes his Civic WTCC will be a more competitive at the Russian venue than it was at the high-speed Salzburgring a fortnight ago.
Tarquini was the only other driver to break into the 1m29s in the opening session, and found a 0.043 second gain in FP2 to edge out Campos Chevrolet racer Hugo Valente by 0.024s.
Valente was one of four customer Chevrolet runners to enjoy a spell at the top of the timing screens in FP2.
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