It was an emotional evening for Cahill, who returned to the ground at which he launched his club career, level on 29 Socceroos goals with Damian Mori.
By the end of the first half the New York Red Bulls attacking star had netted two trademark goals to take his tally to 31 and become Australia's leading scorer.
(Record... Tim Cahill celebrates his historic goal. GETTY)
Australia started well with new captain Mile Jedinak marshalling the troops in midfield.
The Crystal Palace captain had the first shot on goal from a free after five minutes and a minute later Cahill had a header stopped by the Ecuadorean keeper.
Then, at the eight-minute mark, the striker made history by scoring his 30th international goal to become Australia's all-time top scorer, edging ahead of Mori.
Seven minutes later, Gabriel Achillier pulled Cahill's shirt in the box. Jedinak slotted home the resulting penalty to put Australia 2-0 up in the last match before Postecoglou names his 30-man squad for the World Cup in Brazil.
Cahill scored again with a header at the 31-minute mark to make it 3-0.
The striker finished off a perfect cross from Tommy Oar, who'd made a blistering run down the left side.
Curtis Good, the youngest player in the squad at 20 years of age, started in defence, gaining his first Socceroos cap and proving Postecoglou is serious about blooding a new "golden generation".
Good played alongside Matt Spriranovic with both putting in solid performances making a return for former captain Lucas Neill less likely.
The centre back pair didn't play against Costa Rica in November but came in for the overlooked Neill and injured Rhys Williams.
Brisbane Roar defender Ivan Franjic was given the nod for the right back role ahead of veteran Luke Wilkshire.
Mat Ryan went a long way to securing the spot of Australia's leading gloveman heading into Brazil with a near-flawless display in the first 45 minutes making numerous saves.
After halftime, Ecuador came out with a lot more spark and were duly rewarded 10 minutes in when Manchester United winger Antonio Valencia set up Fidel Martinez.
Minutes later, Langerak, who'd came on for Ryan, was shown a red card after rushing off his line and making a crude tackle.
(Off... Mitch Langerak sees red early in the second half. GETTY)
Ecuador's Segundo Castillo made no mistake, pushing the penalty beyond third keeper Brad Jones.
Suddenly it was 3-2 and Australia was a man down.
Postecoglou brought on Alex Wilkinson for Good, Dario Vidosic for Oar and Oliver Bozanic for Cahill as there was a growing sense that it was just a matter of time before the South American side equalised.
It did when a Jedinak mistake in midfield eventually led to an Enner Valencia goal.
With just a minute left and a draw looking likely, disaster struck for the Socceroos when poor defending gifted Edison Mendez the winning goal.
(Joy... Ecuador players celebrate thei winning goal. GETTY)
One of few positive moments for the Australians in the second half came when 21-year-old Massimo Luongo made his debut, coming on for the captain.