AUSTRALIA'S John Millman completed a remarkable comeback to claim a three-set victory over Thiago Monteiro, sending Australia to the Davis Cup finals in Spain.

Millman lost his opening set against Thiago Monteiro in a tie-break as Brazil continued recovering in the tie on Saturday. However, the 30-year-old bounced back to claim the second set sending the match to a decisive third set.

All three sets went to a tie-break, the nailbiter ending in Millman's favour 6-7 7-6 7-6.

Australia now hold an unassailable three-one lead ahead of Jordan Thompson's reverse singles match at Memorial Drive.

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Earlier, Brazil defeated Australia in Saturday's doubles rubber to keep their Davis Cup qualifying tie alive in Adelaide.

Marcelo Demoliner and Felipe Meligeni Rodrigues Alves came from a set down on Saturday to pip Australia's James Duckworth and John Peers in a tense encounter, prevailing 5-7 7-5 7-6 (8-6).

After the final set went to a tie-break, the Australian pair survived four match points and were on the verge of a stunning comeback.

However, the Brazilian duo prevailed, winning the nailbiting encounter in over three hours.

Millman and Thompson won each of their singles rubbers on Friday to give Australia a two-nil lead in the tie.

On Friday, Millman had taken the unlikeliest of Davis Cup victories against Brazilian Thiago Seyboth Wild in a three-set comeback thriller.

World No. 43 Millman was struggling early against the 19-year-old World No. 113, but he held his nerve and mustered a brilliant comeback to claim the victory and give Australia the advantage after the first day in Adelaide.