UPDATE: The Junior Wallabies have ensured a semi-final spot at the U20 world championships after beating a 14-man Ireland 45-17 in Argentina.
After sealing their second successive bonus point win of the tournament, the Aussies were at short odds to top Pool B, with only England able to stop them.
But when they just scraped past Italy by a point hours after Australia's victory over Ireland, the Junior Wallabies' passage to the final four was set.
Ireland can finish on equal points if they beat Italy with a bonus point and England downs Australia but the first tie-breaker in the pool is the head-to-head result, meaning the Junior Wallabies will progress regardless of their result against the Poms.
After winning the Six Nations grand slam and beating England in their opening world championship match, Ireland was ranked among the favourites for the tournament and their clash with the Junior Wallabies was widely expected to decide the pool.
Here's the Pool B standings after round two. The #JuniorWallabies are assured of top spot and a first semi-final since 2011 because even if @IrishRugby match their 10 points, Australia go through on head-to-head rule pic.twitter.com/4920vi0rBM— World Rugby (@WorldRugby) June 8, 2019
Australia opened a 10-0 lead and when Ireland had a player red carded for a high tackle midway through the first term, it seemed as though the Junior Wallabies would waltz through the round easily.
But the Irish dug in and took the lead early in the second half, threatening a win against the odds before a late Australian blitz sealed the match.
The bonus point win handed the Junior Wallabies the lead in Pool B, with just Thursday morning's match against England to come.
Captain Fraser McReight said his team knew it was going to be an arm wrestle against the Six Nations champs.
"We knew it was going to be a grind and hopefully if we played the sort of footy we knew we could play, the back 15 minutes we would hopefully score some points," he said.
"And we did that. We got lucky with the red card but we stuck to our systems and ended up playing some good footy, so I'm really proud of the lads."
And McReight said the effort left Australia confident heading into its final pool clash against England.
"We knew we could play like that and we have great individual players in those positions to make those key decisions," he said.
"Luckily we got some offloads away and scored some brilliant tries, so I'm just really stoked with the lads."
Three tries in five minutes midway through the second half put the Aussies in front before another two in the dying stages allowed the Junior Wallabies to push to a comprehensive victory in Santa Fe.
The Junior Wallabies opened the scoring in the fourth minute, with flyhalf Will Harrison converting a penalty attempt to give Australia a 3-0 lead.
When Semisi Tupou was handed a yellow card in the 15th minute, the Junior Wallabies were a man down but the numbers were even again just five minutes later when Ireland second-rower Ryan Baird was red carded for a high tackle.
Harrison missed the attempt at goal but Australia was in just seconds later when winger Sione Tui crossed, with Harrison's successful conversion giving the Aussies a 10-0 lead.
After being held out for most of the period, Ireland hit back minutes before halftime after captain Charlie Ryan opted for a scrum from a penalty, with halfback Craig Casey scampering over.
Flyhalf Jake Flannery then converted to reduce the margin to just three points.
The Junior Wallabies had a chance to increase their buffer again before the break but Harrison just missed the penalty attempt, shaving the upright, with Australia going to halftime up 10-7.
Ireland may have had just 14 men but they were not about to roll over and the Junior Wallabies were forced to dig in, in the opening stages of the second term, holding a player up over the line as the Irish hammered their line.
But a conceded penalty soon after allowed the Irish to convert a shot and tie the game up and when Stewart Moore crossed just minutes later and his try was converted, the Irish had the lead for the first time in the match.
Playing a man down had taken a toll though and the Junior Wallabies finally broke the dam wall in the final 20 minutes.
They scored three tries in five minutes - through Isaac Lucas, Mark Nawaqanitawase and Nick Frost - to break the game wide open and race to a 31-17 lead.
Frost's try was a beauty, taking the ball from the restart and racing almost 70m to score to put the result beyond doubt.
Michael McDonald missed a penalty in the 70th minute but it did not signal the end of scoring opportunities, with Harrison and Frost scoring tries in the final five minutes to pad out the score.
The Junior Wallabies face England in their final Pool B match on Thursday, June 13, at 4:30am AEST.
Junior Wallabies 45
Tries: Nick Frost 2, Sione Tui, Isaac Lucas, Mark Nawaqanitawase, Will Harrison
Cons: Will Harrison 6
Cards: Sione Tui (yellow 15')
Tries: Craig Casey, Stewart Moore
Cons: Jake Flannery, Ben Healy
Cards: Ryan Baird (red 20')