A combination of Ryan Baird's 21st-minute red card and a luckless spate of injuries left the Ireland Under-20s exposed down the final stretch as Australia ruthlessly took advantage to claim a 45-17 bonus point win in Santa Fe.
The Junior Wallabies ran riot with five closing tries - racking up a mammoth 35 points during the final 17 minutes - to give a lopsided look to what had been a gripping contest between the two leading teams in Pool B of the World Rugby U-20 Championship.
Ireland lock Baird was sent-off for a neck-high tackle on Will Harrison, following on from a similar challenge by Semesi Tupou which earned the Australian centre a yellow card. Craig Casey's try from a quick tap cut the gap to 10-7 for half-time.
Casey's half-back partner Jake Flannery drew Noel McNamara's side level with a penalty before a terrific individual try by Ulster Academy centre Stewart Moore, who beat four defenders from halfway, made it 17-10.
However, 14-man Ireland ran out of gas during the final quarter - with key men Casey and Dylan Tierney-Martin having to be replaced - as the Australians cut loose out wide, stretching clear thanks to converted tries from Isaac Lucas, Mark Nawaqanitawase, Nick Frost (2) and out-half Harrison.
Although Ireland's semi-final hopes have taken a considerable hit, captain Charlie Ryan was remaining positive and said afterwards: "It was always going to be tough to beat Australia with 14 men, but we're going to bounce back from this. It's still all to play for in the pool.
"Obviously playing with the 14 men for 60-odd minutes, it's always going to be really tough. We're going to have a good look back at it, review the video and look forward to the Italy game next Wednesday. We have to get the result there and see where it leaves us."
Harrison nudged the Junior Wallabies ahead with a sixth minute penalty, rewarding Angus Bell’s pressure at a scrum, and they foiled Ireland’s first visit to the 22 which saw Flannery release Angus Kernohan down the right wing.
Getting back on the attack thanks to Tierney-Martin’s breakdown skills, Ireland were unable to take advantage of Tupou’s sin-binning for a high tackle on John Hodnett - and they were down to 14 men themselves entering the second quarter.
As Australian out-half Harrison juggled a pass, Baird caught him high around the neck and referee Christophe Ridley produced his red card following a TMO review. Harrison missed a subsequent penalty but a crisp attack out to the left played in winger Sione Tui for a well-worked converted try.
Nonethless, Ireland snapped back with some of their best attacking phases of the first half. Liam Turner sped through a gap with busy full-back Rob Russell increasing his influence on his first start in the green jersey.
David McCann, the two-try hero from the England game, began to make yards, aided by fellow Ulsterman Moore’s spinning out of two tackles. Australia leaked two penalties and a free-kick near their line before scrum half Casey burrowed over from a quick tap.
Ireland benefited from the referee’s on-field decision of the ball being grounded ahead of the TMO consultation, and with the score standing, Flannery’s conversion made it a three-point game. It stayed that way with Harrison missing a late penalty after Flannery had infringed when attempting to clear a ruck.
Resuming for the second period, McNamara’s charges emerged back into the sunshine looking the better team. They went for the jugular as the Junior Wallabies conceded three successive penalties close to their line, which only drew a warning from the referee.
Hodnett and McCann were both held up from close range, and despite a messy scrum allowing Australia to clear, a penalty reversal for goading by an Australian player allowed Flannery to kick Ireland level from a central position.
The Grand Slam champions grasped the lead soon after, Moore showing his class off a scrum on halfway as he fended off Michael McDonald, stepped inside Harrison and evaded two more tacklers on a barnstorming 57th-minute run in to the left of the posts.
Replacement Ben Healy comfortably converted but that proved to be Ireland’s final score as they endured a nightmare finish. Ryan led a choke tackle which briefly broke up Australia’s momentum, but the Oceania U-20 champions had a lot more in the tank.
Twice they exploited space on the outside, Tupou charging through to set up Lucas’ levelling score before the speedy full-back turned provider, supplying a return pass for Nawaqanitawase to dive over in the right corner.
The killer blow came straight from the restart which Ireland slightly overshot, allowing fresh-legged receiver Frost to burst clear from outside the Australian 10-metre line, handing off Flannery on his way to a superb bonus point try, again converted by Harrison.
Ireland dug in with replacements Michael Milne and Cormac Foley combining at a ruck to win a relieving penalty. Another breakdown decision went their way, Healy’s right boot driving them into prime maul position only for Australia to quickly claw back turnover ball.
A flattering late gloss was put on the scoreboard when a ruck ball squirted loose and Harrison scampered clear for the penultimate try. Big second row Frost completed his brace thanks to a snappy break and pass by fellow replacement Carlo Tizzano.
Isaac Lucas (Sunnybank); Sione Tui (Melbourne Unicorns), Semisi Tupou (Box Hill), Noah Lolesio (Tuggeranong Vikings), Mark Nawaqanitawase (Eastwood); Will Harrison (Randwick), Michael McDonald (Palmyra): Angus Bell (Sydney University), Lachlan Lonergan (Tuggeranong Vikings), Josh Nasser (University of Queensland), Michael Wood (Brothers), Trevor Hosea (Harlequins Rugby Club), Harry Wilson (Brothers), Fraser McReight (Brothers) (capt), Will Harris (Eastern Suburbs).
Replacements used: Nick Frost (Queanbeyan Whites) for Wood (56 mins), Pat Tafa (Northern Suburbs) for Harris (72), Esei Ha'angana (Melbourne Unicorns) for Hosea (73), Rhys van Nek (Easts) for Lonergan, Joey Walton (Gordon) for Lolesio, Carlo Tizzano (University of Western Australia) for McReight, Kye Oates (University of Queensland) for Tupou (all 78).
Rob Russell (Dublin University/Leinster); Angus Kernohan (Queen's University/Ulster), Liam Turner (Dublin University/Leinster), Stewart Moore (Malone/Ulster), Jonathan Wren (Cork Constitution/Munster); Jake Flannery (Shannon/Munster), Craig Casey (Shannon/Munster); Josh Wycherley (Young Munster/Munster), Dylan Tierney-Martin (Corinthians/Connacht), Thomas Clarkson (Dublin University/Leinster), Charlie Ryan (UCD/Leinster) (capt), Ryan Baird (Dublin University/Leinster), David McCann (Banbridge/Ulster), Ronan Watters (St. Mary's College/Leinster), John Hodnett (UCC/Munster).
Replacements used: Ciaran Booth (Sale Sharks/IQ Rugby) for Watters (18 mins), Ben Healy (Garryowen/Munster) for Russell, Michael Milne (UCD/Leinster) for Wycherley (both 56), John McKee (Old Belvedere/Leinster) for Tierney-Martin, Colm Reilly (Buccaneers/Connacht) for Casey (both 60), Niall Murray (Buccaneers/Connacht) for Hodnett, Cormac Foley (St. Mary’s College/Leinster) for Moore (both 64), Declan Adamson (Clontarf/Leinster) for Wren (72).
Scorers for Australia: Tries: Sione Tui, Isaac Lucas, Mark Nawaqanitawase, Nick Frost 2, Will Harrison; Cons: Will Harrison 6; Pen: Will Harrison
Scorers for Ireland: Tries: Craig Casey, Stewart Moore; Cons: Jake Flannery, Ben Healy; Pen: Jake Flannery
Christophe Ridley (England)
6 minutes – Australia penalty: Will Harrison – 3-0; 15 mins – Australia yellow card: Semisi Tupou; 21 mins – Ireland red card: Ryan Baird; 24 mins – Australia penalty: missed by Will Harrison – 3-0; 25 mins – Australia try: Sione Tui – 8-0; conversion: Will Harrison – 10-0; 36 mins – Ireland try: Craig Casey – 10-5; conversion: Jake Flannery – 10-7; 40+2 mins – Australia penalty: missed by Will Harrison – 10-7; Half-time – Australia 10 Ireland 7; 55 mins – Ireland penalty: Jake Flannery – 10-10; 57 mins – Ireland try: Stewart Moore – 10-15; conversion: Ben Healy – 10-17; 63 mins – Australia try: Isaac Lucas – 15-17; conversion: Will Harrison – 17-17; 65 mins – Australia try: Mark Nawaqanitawase – 22-17; conversion: Will Harrison – 24-17; 67 mins – Australia try: Nick Frost – 29-17; conversion: Will Harrison – 31-17; 70 mins – Australia penalty: missed by Michael McDonald – 31-17; 77 mins – Australia try: Will Harrison – 36-17; conversion: Will Harrison – 38-17; 79 mins – Australia try: Nick Frost – 43-17; conversion: Will Harrison – 45-17; Full-time – Australia 45 Ireland 17