By Gabriel Tan at the Jalan Besar Stadium
Following a goalless first half, Duric - who also netted in the first leg - opened the scoring in the 78th minute when he strongly held off a Park Min-ho's challenge before firing home to all but kill off their opponents' hopes.
Five minutes later, the Singapore international netted his second from close range, before Imran Sahib added a third in injury-time to cap off an excellent night for the visitors.
The result also ended Loyola's brave run in their debut appearance in the competition, although they can return to the Philippines with their heads held high after some excellent displays, including victories over Geylang United and Kanbawza in the earlier rounds.
Heading into Sunday's game needing goals if they were to have any chance of progressing to the final, the Sparks named an attack-minded starting XI including captain James Younghusband and Mark Hartmann, who were both on the bench in Thursday's first leg.
Just five minutes in, they carved out their first chance when Jang Jo-won latched onto a long ball and ghosted past Anaz Hadee, only to see his effort kept out by Sasa Dreven.
Tampines wasted an excellent chance to open the scoring in the 13th minute when Noh Alam Shah blazed over unmarked from four yards, after Gligor Gligorov broke free down the right and whipped a good cross into the box.
Four minutes later, Loyola themselves had a good opportunity when Philip Younghusband picked out Jang with a glorious cross-field pass, who in turn laid it off to Hartmann after jinking past Anaz. However, with all the time in the world to line up his shot, the 20-year-old could only roll the ball on his wearker left foot straight at Dreven.
The Croatian goalkeeper, who has struggled for consistency all season long, then made a stunning save in the 28th minute to keep the scores level after tipping away a blistering strike from Philip Younghusband from the edge of the area.
Four minutes later, the younger of the Younghusband brothers was again left wondering how he had failed to score after meeting a cross from his brother James with a sweetly-struck snapshot, only to be denied by a stunning reflex stop from Dreven.
With their opponents looking increasingly likely to grab a goal - and get back into the tie - the Stags started to play with more intent and it was Ref Cuaresma's turn to come to his side's rescue, pushing away a low drive by Sead Hadzibulic in the 35th minute.
A minute later, the Philippines international produced an even-better save to keep out a fierce half-volley by Alam Shah, after Hadzibulic had leapt high inside the area and nodded the ball to him.
Despite having a relatively-quiet opening period, Duric began to come to life after the break and gave the opposition defence a warning in the 54th minute when he forced his way past Alexandro Elnar and into the box, although no one was on hand to meet his delicate ball across the face of goal.
Eight minutes after the hour mark, Dreven had to be alert once more as he raced out of his area to head away a long ball by Hartmann before James Younghusband could pounce, and it began to look as though Loyola's pressure was soon going to reap rewards.
However, the United Football League outfit's hopes were all but ended twelve minutes from time when Jamil Ali, who was brought on just three minutes earlier for the ineffective Alam Shah, tore down the left and crossed the ball to Duric, who brushed off Park's attentions before clinically blasting a shot past Cuaresma.
Three minutes later, Jamil wasted a chance to get one of his own as he strode through the middle and exchanged passes with Imran, only to miscue his shot and send it trickling harmlessly wide.
Nonetheless, the tricky winger needed just two minutes to make amends when he laid on another assist for Duric. Once again finding space down the wing, Jamil raced into the box and forced Cuaresma to come out and confront him, before slipping a pass to his captain, who expertly squeezed a shot past his marker and inside the near post.
To the Sparks' credit, they continued to push forward in search of a consolation to give the large number of Filipino supporters, but that left plenty of gaps at the back, which Tampines exploited in injury-time.
Picking up possession down the left, Jamil went on another terrific run and left two men in his wake, and with several team-mates charging forward in support, he picked out the right option in sliding the ball to Imran, who sent an emphatic effort into the roof of the net to hammer the final nail in the Loyola coffin.
Loyola Meralco Sparks: Ref Cuaresma, Alexandro Elnar, Chad Gould, Park Min-ho, Roxy Dorlas (Peter Fadrigalan 83'), Andres Gonzales, Simon Greatwich, Mark Hartmann, James Younghusband, Jang Jo-won (Jake Morallo 79'), Philip Younghusband.
Tampines Rovers: Sasa Dreven, Anaz Hadee, Mustafic Fahrudin, Jufri Taha, Imran Sahib, Ahmad Latiff, Gligor Gligorov, Ismadi Mukhtar, Aleksandar Duric (Ahmed Fahmie 86'), Sead Hadzibulic (Sazali Salleh 60'), Noh Alam Shah (Jamil Ali 75')