The defeat came despite Speed sending out a strong starting XI boasting the likes of Aaron Ramsey, Craig Bellamy and Gareth Bale, and represented Speed's fourth loss in five games since taking over the national side.
In addition to Cahill, Australia delivered Premier League quality in the form of Blackburn's Brett Emerton and Fulham goalkeeper Mark Schwarzer. Former West Ham, Blackburn and Everton defender Lucas Neill was also in the their starting line-up.
The first half was slow to get going, with both sides failing to ignite a sparse crowd. Australia's Luke Wilkshere looked the most likely; the full-back finding himself plenty of space on the flank to send over a succession of crosses.
Bellamy enjoyed plenty of the ball for Wales, but for all his hard graft only managed to deliver one effective ball into the middle. Ramsey was also a central figure, but in truth the Arsenal midfielder looked rusty and an unconvincing outing ended with him being substituted at half-time - perhaps with the weekend's Premier League action in mind.
But while Wales dominated possession, they failed to create a single meaningful chance in the first 45 minutes – all too often faltering with their final ball under pressure from Australian defenders.
It was a similar story with Australia, before Wilkshere's fierce drive on 35 minutes hit the post and seemingly kick-started their attacking ambition. Just under 10 minutes later the visitors went ahead when Cahill met Wilkshere's cross with a crisp volley on the turn to give Wayne Hennessey no chance in the Wales goal.
Australia came painfully close to doubling their lead shortly after the break. Hennessey did well to block Kruse's low shot, then Carl Valeri saw his follow-up effort hit the post.
On the hour mark the visitors deservedly got a second. Cahill played in Scott McDonald on the right, and when his cross was palmed away by Hennessey Kruse was on hand to tap home from close range.
As both sides made a raft of substitutions the game began to open up and Wales gave themselves hope when Blake collected his first international goal on 82 minutes - heading home from 12 yards after Australia failed to deal with a bouncing ball in the box.
The goal sparked Wales into life. Suddenly their attacking play had a purpose and the previously rock-solid Australian defence began to look vulnerable. But time was not on their side. Substitute Jack Collison came closest with a left-footed shot from the corner of the box, but ultimately Wales had left it too late.
The final whistle continued Speed's poor run since taking over in December last year. With Wales languishing at the bottom of their Euro 2012 qualifying group, and in 112th place on the FIFA rankings, it certainly wasn't the pick-me-up a nation had needed.
Montenegro and England are next for Wales and Speed, and they'll need to reproduce the intensity they showed in the final 10 minutes in Cardiff to stand any hope of avoiding two further defeats.