Andy Murray falls at first hurdle at Brisbane International

The unseeded Murray was on course to advance after taking the opening set of a tense battle between two former tournament champions on Pat Rafter Arena.

But Dimitrov hit back to progress 4-6 7-5 6-2 and inflict another early exit on Murray following his second-round victory when the pair met at last year's US Open.

The world number 14 will face either Australian qualifier Li Tu or Germany's Daniel Altmaier in round two.

Murray was playing his first competitive singles match since a first-round loss to Alex de Minaur at the Paris Masters in late October after a shoulder injury ruled him out of representing Great Britain in the Davis Cup finals.

The 36-year-old initially impressed during a tight encounter which remained on serve until he capitalised on an error-strewn 10th game from his opponent to clinch the opening set.

But Dimitrov calmly responded to force a decider by edging a more chaotic second set which ended with both players struggling to hold serve.

The Bulgarian's efforts to level were aided by saving a crucial break point with a stunning baseline smash while playing with a broken string.

Three-time grand slam champion Murray was visibly annoyed by the momentum shift and offered little resistance in a relatively one-sided final set as Dimitrov won in just under two-and-a-half hours.

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