Serbia seized control of their Davis Cup World Group playoff against Australia with a victory in the all-important doubles rubber.

Untried before as a Davis Cup pairing, Novak Djokovic and Nenad Zimonjic sparked scenes of hysteria inside the mammoth Beogradska Arena with a magical four-set win over Lleyton Hewitt and Paul Hanley.

Djokovic and Zimonjic recovered from a nervy and hesitant start to prevail 3-6 6-4 6-3 6-2 in two hours and 52 minutes to give Serbia a 2-1 advantage in the best-of-five-match tie.

Australia, the second-most successful country in Davis Cup history, must now win both of Sunday's reverse singles rubbers to avoid relegation from the elite 16-nation World Group for only the second time.

And they will start underdogs in both.

Hewitt opens up against world No.3 Djokovic and should he upset the US Open runner-up, world No.91 Peter Luczak will take on the 53rd-ranked Janko Tipsarevic in the decisive fifth rubber.

If Serbia win either match, the tiny war-torn country will be promoted to the World Group for the first time as an independent nation.

For the first set and a half, the Serbs looked like they would need two points on the last day.

Hewitt and Hanley were giving Djokovic and Zimonjic a lesson in the art of doubles, dominating the net exchanges and generally looking much more assured than the Serbs.

The Australians broke both Serbs' service to take the first set comfortably before maintaining the momentum by breaking Djokovic again to go 2-0 up in the second.

But it was all down hill from there as Zimonjic, in particular, grew in confidence after looking all at sea early in front of the record 19,662 mostly pro-Serbian fans.

After holding his first five service games, Hanley was suddenly broken twice in a row, and it was the only invitation into the contest the locals required.

After levelling at a set apiece, the inspired Serbs broke Hanley again in his first game of the third set for a 2-0 lead.

Try as they might, the Australians were unable to make any inroads on either Djokovic's or Zimonjic's serve for the rest of the set and quickly found themselves down two sets to one.

It was all but over after Hanley and Hewitt were both broken early in the fourth as the Serbs surged to a 4-0 lead.

Djokovic completed the formality when he calmly served it out to love and leave Serbia well and truly in charge of the tie.

Hewitt lamented not being able to twist the knife when they seemingly had the Serbs at their mercy in the second set.

"We had a lot of chances early in the second set and couldn't quite get them. We could have easily been up a double break early in the second," he said.

"To their credit, though, they hung in there and served well on the big points and got out of a couple of those tight games.

"Then we played one loose game to give back the break and the momentum really swung after that.

Hewitt was not giving up all hope of Australia pulling off a miraculous comeback win and said a key against Djokovic was trying to limit the fervent crowd's influence on proceedings.

"It'd be nice to get on top early, but it's easier said than done," he said.

"I've got to try to find a way to do that. We'll just see what happens."

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