A near-perfect week for Australia's tennis men at the Davis Cup has crumbled on the final day, as they endured two painful near-misses in a 2-1 defeat to hosts Spain in Valencia.

Captain Lleyton Hewitt said he was proud of his team even in defeat, revealing the physical lengths players went to in order to front up for this week's ties.

"We've had a few guys this week pretty banged up — and it's only really our locker room knows that.

"It would have been very easy for a few of my boys to not turn up this week, but they've come and they put on the green and gold, and done absolutely everything I've asked of them. I'm super proud."

Purcell played in the doubles in Tuesday's opener against France less than three days after winning at Flushing Meadows, but was struggling in Sunday's deciding rubber alongside Matt Ebden as the former Wimbledon champs went down to a shock defeat.

"To try and ask players to play the second day after a grand slam finishes, it's not easy," said Hewitt.

"In the old (weekend only) format, I used to have to do it, but you'd at least have until the Friday before you had to play. Now to play on Tuesday, it's ridiculous."

Hewitt also couldn't see any sense in the week-long, four-team group stage ending with two already-qualified teams playing what, to all intents and purposes, was a dead rubber.

"That's the stupid part of this format, isn't it? You know, I can keep saying it," Hewitt said.

"But the format is what it is, and we'll do what we need to do to get through and give ourselves a chance of hopefully holding up the trophy."

With both sides' place in November's finals already safely booked after they had won their ties against France and the Czech Republic earlier in the week, there was, in theory, only pride to play for in the final group B clash.

Yet it certainly didn't feel that way as the home side, even without their rested superstar Carlos Alcaraz and cheered on by a wildly enthusiastic full-house in the Pabellon Fuente de San Luis, defied all the odds to battle to a win that ensured they topped the group.

Jordan Thompson had served for the match in the opening rubber, only to go down 2-6, 6-2, 7-6 (7-3) to veteran Spanish substitute, the much lower ranked Pablo Carreno Busta, in what the Sydneysider described as an "incredibly frustrating" reverse.

But Spanish captain David Ferrer's decision to rest Alcaraz for the battle of the teams' top singles players then paved the way for Alexei Popyrin to level the tie with a fairly routine, crowd-silencing 6-4, 6-4 victory over Pedro Martinez.

It set up a doubles decider, with the Aussie pair of Matt Ebden and Max Purcell, who boast an outstanding Davis Cup record, the hot favourites to prevail over the home duo of Marcel Granollers and Martinez.

With the odds stacked against them, especially with Martinez having to come back on court so soon after his defeat, things looked even more bleak for the Spaniards as they lost the opening set to the former Wimbledon champs, Ebden and Purcell.

But inspired to new levels by the din at the indoor hardcourt venue, 38-year-old Granollers, the world's number one, helped the occasional doubles player Martinez to a remarkable 5-7, 6-4, 6-4 win.

AAP