Araujo’s fellow Brazilian Fernandão and Iraq star Nashat Akram also got on the score sheet while Ali Karimi netted a consolation for the Iranians in the Group B clash at Al Gharafa Stadium.
Only a win would keep Al Gharafa's hopes of reaching the knockout stages alive and they fired an early warning of their attacking intentions after four minutes when Piroozi keeper Ali Reza Haghighi parried Shami Zaher's looping shot.
Three minutes later, striker Fernandão produced a sharp header from close range but Haghighi was again equal to the task.
However, Al Gharafa took the lead in the eighth minute when skipper Saad Al Shammari chipped a cross towards Fernandão inside the box and the Brazilian produced a spectacular overhead kick to find the back of the net.
Karimi tried to imitate Fernandão five minutes later but the Iranian international's weak effort dribbled past the post.
Al Gharafa nearly doubled their lead in the 28th minute as midfielder Akram met Ahmed Fares ' cross but his close-range effort was well saved by Haghighi.
Piroozi nearly scored a spectacular equaliser when Mazyar Zare unleashed a thunderbolt from 35 yards which hit the post, much to the dismay of a large Iranian contingent inside Al Gharafa Stadium.
Al Gharafa then took the game away from the visitors as half-time approached.
Araujo's deft touch from close range following Al Shammari's pass one minute before the break gave the home side a two-goal lead and shortly after, he headed home following a mistake from the Piroozi keeper.
Haghighi's fumbled Akram's shot from the edge of the box and Araujo expertly nodded in from close range two minutes into stoppage time.
Al Gharafa scored their fourth in the 69th minute, Akram finishing clinically from close in before Karimi's header at last gave Piroozi's fans something to cheer about seven minutes later.
But Araujo completed his treble with 10 minutes remaining, the striker baring down on goal before calmly slotting past the onrushing Haghighi to complete the rout.
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Al Gharafa coach Marcos Paqueta could barely contain his delight after watching his side annihilate Piroozi 5-1 at Al Gharafa Stadium.
Araujo proved the hero with a hat-trick as the recently-crowned Qatar league champions hauled themselves firmly back into contention in Group B for a place in the knockout stage.
It was also sweet revenge for Paqueta after the 3-1 defeat against the same side at the Azadi Stadium last month.
“It is a memorable day for Al Gharafa,” he said.
“We played a great match against a very good side. We wanted a positive result from this match but this is even better. I think we finally got the balance right in our team. I congratulate the team on this great performance.
“We are trying to improve in every match. That is because my players are motivated to do well (after winning the Qatar League).”
Paqueta also revealed he had told his players to focus on the task in hand and they responded in fine style.
“We had a couple of injuries but we started with our best 11. I had told my players to stop celebrating (the victory in the Qatar Stars League) as we have important matches coming up,” he added.
“We are playing the AFC Champions League so this is a very important tournament for us. This is Asia’s best football tournament.”
Piroozi coach Nelo Vingada, meanwhile, had no complaints about the result, admitting his team had been outclassed.
“Al Gharafa played really well,” he said.
“They showed why they are the champions. We beat them 3-1 at the Azadi Stadium so we came here looking for three points. We couldn’t do it, we remember how they fought till the last minute in the first match.”
The result means Al Shabab and Piroozi are level at the top of Group B on seven points apiece but with Al Gharafa now just one behind, the race for the two places in the knockout phase is wide open.
Vingada, though, was only looking as far as their next encounter against Al Shabab.
“We are not thinking about the next stages,” he added.
We are only taking one match at a time. There are many important matches left so we can’t start thinking about matches that will be played later.
“Our main focus is on the AFC Champions League. I knew this was going to be a pressure game but if you have the players to do it, then you don’t have to worry. We had brought a strong squad here and started with our best 11.”