After Alexei Popyrin had been on the end of a shock 7-6 (7-5) 7-5 defeat from Borna Gojo - a late stand-in ranked more than 200 places behind him - Australian No.1 Alex de Minaur saw his excellent comeback attempt thwarted 6-1 5-7 6-4 by old foe Cilic.

It sealed the Croatians' victory with the Australians so desperate to get something out of Thursday's tie that they later threw de Minaur, after only a short break, into the doubles.

The move singularly failed to pay off, though, as de Minaur, who stepped in for Alex Bolt, was outplayed alongside John Peers, with the Aussie pair being blitzed 6-3 6-1 by a consummate performance from the world's No.1 pairing, Olympic champions Nikola Mektic and Mate Pavic.

Not even the vociferous courtside encouragement of captain Hewitt in the Pala Alpitour could lift his side and though all is not quite lost, Australia will almost certainly have to beat Hungary 3-0 on Saturday to have a chance of making the quarter-finals, even then only as one of the best second-placed outfits.

"It's obviously disappointing, not the way we would have liked to start the campaign but mathematically it's possible (to still qualify)," said Hewitt.

"We get the opportunity to play another match for Australia and wear the green and gold and it doesn't matter if we can make it or not, we're going to leave absolutely everything out there on the court in those three matches."

De Minaur pulled out some of the magic that had seen him go unbeaten in singles in the last edition of the men's World Cup of tennis two years ago as he fought back from 6-1 3-1 down and even took a 2-0 lead at the start of the decider.

But he was crestfallen at not being able to consolidate that early break. "I dug deep ... but not being able to get that point for Australia really hurts me," he said.

The 33-year-old Cilic, who'd defeated de Minaur in a US Open thriller three years ago, rediscovered his irresistible, crushing form of the opening set to oust the Sydneysider in a topsy-turvy but compelling two hours 10 minute affair.

Popyrin, the world No.61, had earlier been expected to give the team a flying start against the depleted Croats, who plunged world No.276 Gojo into the singles at late notice.

Yet the big-serving understudy, filling in for injured luminary Borna Coric, produced the performance of his life to prevail over one hour and 49 minutes.

"This was probably the most painful loss I've had," said the 22-year-old Popyrin, sounding a little emotional.

"I had chances in the first and second sets but I did hit some mistakes on important points and I think that let me down."

Popyrin started confidently but after earning five break points on Gojo's big delivery in the Croat's first three service games, his failure to convert came back to haunt him.

Popyrin played a poor opening set tiebreaker, featuring a series of unforced errors that cost him the stanza but, despite gifting up 27 unforced errors throughout the match, he had not been remotely threatened on serve until the 11th game of the second set.

A nervy double fault and a stray long backhand suddenly gave Gojo the chance to serve for the match, which the 23-year-old took with aplomb.

Australian Associated Press