Technology could have broken England's last stand of resistance in the fight to keep Australia from claiming the Ashes urn.
The hosts had set the tourists the improbable target of 504 for victory in the third Test at the WACA Ground.
And despite some early setbacks England showed fight with a 99-run partnership between Ian Bell and rookie Ben Stokes.
But Bell was dismissed for 60, and England at 5-220, when Australia challenged a not out decision for caught behind.
Snicko, the sound recording that ahs already caused controversy in this fixture, indicated Bell had hit the ball and the decision of umpire Marais Erasmus was overturned and the England right-hander returned the pavilion.
England finished the day on 5-251, still needing 253 to win the match. Or they have to bat out three sessions to draw the contest and keep a slight grip on the Ashes.
Earlier in the final session Kevin Pietersen threw his wicket away as England looked likely to surrender.
Pietersen's impetuosity got the better of him shortly after tea when he couldn't resist the urge to belt spinner Nathan Lyon only to put the ball down the throat of Ryan Harris on the long-on boundary.
England slumped to 4-121.
Highlighting England's perils, they lost skipper Alastair Cook, dismissed first ball by a Ryan Harris ball that took his middle and off stump.
Joe Root and Michael Carberry took the score to 62 before Carberry was trapped lbw by Shane Watson for 31.
A brilliant Brad Haddin catch then removed Root off Mitchell Johnson for 19, Haddin flinging himself to his right to take the catch in front of Watson at first slip.
Earlier Watson raced to a 107-ball century and George Bailey took 28 of a Jimmy Anderson over before skipper Michael Clarke called the Australian batsmen in at 6-369 after the lead had gone past 500.
Watson launched a brutal assault on the English attack in Monday’s opening session, going on the offensive from the first over of the day. He took just 29 balls to race from fifty to 100, his fourth test hundred.
Resuming on 29, with Australia 3-235 and already nursing a lead of 369, Watson made his team’s intentions clear from the first over of the day when he smacked English off-spinner Graeme Swann down the ground three times for two fours and a six.
If Swann thought that was bad, he went for three sixes and a four a few overs later as Watson raced into the eighties and the Australians rushed to set up a declaration before the luncheon break.
England gained some brief respite when Ben Stokes had Steve Smith caught at deep mid-wicket by substitute Johnny Bairstow but Watson continued the onslaught as the lead scurried past 400.
Watson’s dismissal, on 103, after Australia had added 96 runs in an hour, summed up England’s bumbling form in this Ashes series.
Trying to launch Tim Bresnan over the boundary for a sixth six, Watson hit the ball straight up in the air and started making for the pavilion, only to make a desperate run for the other end when Ian Bell at cover dropped the catch.
Fortunately the alert Bresnan saved England from further embarrassment when he threw the stumps down at the bowlers end with Watson well out of his ground.
Bailey was unbeaten on 39 after hitting Anderson down the ground for six three times in the last over of the innings, taking a record equalling 28 from the over.