Australia opened up an unbeatable 3-0 lead over Morocco by winning Saturday's doubles match in their Davis Cup playoff at Perth's Royal Kings Park.

Todd Woodbridge and Wayne Arthurs defeated Mounir El Aarej and Mehdi Tahiri 7-6, 7-6, 6-3 to ensure Australia remain in the World Group next year while Morocco are relegated to the next tier.

The home side were strong favourites to wrap up the tie after Arthurs and Lleyton Hewitt won the opening singles matches on Friday but they had to work much harder than expected.

El Aarej and Tahiri were thrust into the tie after Morocco's two best players, Younes El Aynaoui and Hicham Arazi, pulled out, and the pair gave their more experienced rivals a stiff examination.

The Moroccans had three set points in the opening tiebreak but failed to convert their chances and had two break points in the second set which they also wasted.

They successfully fought off eight break points in the first two sets but were unable to stop the Australians, who were better suited to the grass surface.

"This is a substantial win," Australia's non-playing captain John Fitzgerald told reporters.

"On paper it looked like a foregone conclusion but it never works out like that when you step on the court."

Woodbridge, who earlier this year became Australia's longest-serving Davis Cup player, said the Moroccans had caused problems.

"They served really well and we struggled a bit with our returns," Woodbridge said. "They weren't scared, they really performed admirably for their country."

The tie finishes on Sunday with the reverse singles.