Humbled by 381 and 218 runs in the first two tests of the five-match series, England will be forced to hand over the Ashes to the Australians if they capitulate in the third test in Perth this week.
That would mark quite a comedown for a squad which arrived in Australia on the back of a 3-0 win in the first series of the year back home and looking for a fourth successive Ashes triumph for the first time in more than a century.
Now written off by the media - former test opener Geoffrey Boycott said they faced "annihilation" - England must try to revive their fortunes at a WACA ground where they have won just one match in 43 years of test cricket.
"This isn't the time for mincing words, positive this and positive that, sometimes you've got to look at yourself straight in the mirror and know where you're at," he told reporters in Perth on Wednesday.
"That's as an individual, and from a team point of view, and if you don't do that, you carry on doing the same things and getting the same results and we can't afford to do that.
"This is a time for brutal honesty and fronting up."
Prior showed the way with a battling 69 from 102 balls in the second innings in Adelaide but it was nowhere near enough to save the test after England's batting collapse in the face of a Mitchell Johnson barrage in the first innings.
"It's all well and good me sitting here and talking about it but we've got to go out there and deliver," Prior said.
"We need batters scoring big hundreds, bowlers taking wickets and fielders diving on every ball."
Prior said England must approach the Perth test, which starts on Friday, as if it was the start of a new series and was emphatic that the Ashes were not already lost.
"One thing I do know about this team is that when we get to this place we come out fighting. You have no option," he said.
"You can sit there and sulk, moan, whinge and make excuses - but you will just get beaten. You have to get rid of all that and fight.
"Everything is against us, people have written us off, we're at Perth where we haven't won for however many number of years, that, quite frankly, excites me," he added.
"Records are there to be broken, there is a huge amount of hunger in this dressing room to turn it around in this test match."
England captain Alastair Cook has come in for a huge amount of criticism, not least for his loss of personal form with the bat, but Prior said history would vindicate him.
"He will be one of - probably the greatest England cricketer, in my mind there is no doubt about that," said Prior.
"And from a leader point of view, there's no other man that I'd want leading us out there, because one thing he does do is lead by the front and lead by example."