By Gabriel Tan
Despite a less-than-impressive warm-up campaign, which included defeats to Vietnam and Thailand and draws with Hong Kong and Bangladesh, Harimau Malaya, as defending champions and co-hosts, were expected to see off their arch-rivals.
But they were left stunned as Shahril Ishak netted two clinical strikes to given the Lions a commanding lead at the break, before Aleksandar Duric came off the bench and added a third to seal an impressive victory.
Having seen Indonesia surprisingly held to a 2-2 draw by Laos earlier in the day, both sides entered the game knowing a win would put them in pole position to qualify for the semi-finals, even at such an early stage.
Five minutes in, Singapore nearly got off to a dream start when Shahdan Sulaiman whipped a dangerous ball into the box that was met by Baihakki Khaizan, but he failed to strike the ball cleanly and allowed the opposition backline to clear their lines.
Three minutes later, Norshahrul Idlan Talaha showed why he was named Malaysia's best player a few weeks ago when he called Izwan Mahbud into a smart save at the near post, after forcing his way down the right and into the box before hitting a firm shot towards goal.
Despite the early chances, both sides were understandably playing with caution given the high-stakes nature of the tie, and the game gradually evolved into an arm wrestle.
However, that all changed two minutes after the half-hour mark when the Lions stunned the home fans by taking the lead, after Shahril sneaked ahead of Azmi Muslim and latched onto a lovely cross by Shaiful Esah before lifting the ball over the onrushing Fahmi.
That goal certainly reduced the roar of the Harimau Malaya crowd to a whimper but seven minutes before the break, Bukit Jalil was silenced as the visitors doubled their lead.
There appeared to be no apparent danger when Shahdan swung a freekick into the box but Fahmi inexplicably punched it towards in his own goal, and although the recovering Fadhli Shas saved his keeper's blushes by clearing the ball off the line, Shahril was on hand to nod home the rebound and put the Lions 2-0 up.
Things could have gotten even worse for Malaysia five minutes later when Khairul Amri burst through on goal after cleverly flicking the ball over Aidil Zafuan's challenge, only to push the ball too far ahead of himself and allow Fahmi to gather.
Seven minutes after the break, Shahril was almost presented with a chance to complete his hat-trick when a speculative clearance from Daniel Bennett almost sent him through, but thankfully for the hosts, Aidil was on hand to weigh in with a vital interception.
Two minutes before the hour mark, Wan Zack Haikal, who was thrown on by Rajagobal at the break, had a chance to pull one back when a cross was cleared straight to him, but Safuwan Baharudin was on hand to deny him with an important block.
Four minutes later, Norshahrul, who was trying his best to create something with too few supporters, barged Bennett off the ball and whipped in a cross, but there was no one to meet it inside the box.
Malaysia were beginning to look increasingly dangerous and in the 70th minute, Mahalli Jasuli linked up well with Harimau Muda team-mate Wan Zack down the right before floating a cross into the six-yard box, but Izwan did well to gather bravely despite Safee Sali sliding in at his feet.
Nonetheless, Harimau Malaya's increasingly adventurous ways started to leave gaps at the back for their opponents to exploit and three minutes later, Aidil had to be alert to deny Shahril a shooting chance again, after the Lions skipper had exchanged a one-two with Amri and found space inside the area.
Still, the hosts only had themselves to blame two minutes later when Duric, who had only been on the field for a minute, was left completely unmarked inside the area and met a Shahdan cross with a firm header past Fahmi for Singapore's third.
By now, the contest was well and truly over but Malaysia could have given their fans something to cheer about in the 83rd minute when S. Kunanlan flicked a corner to the waiting Aidl on the edge of the area, but the centre-back's blistering strike was smartly stopped by Izwan.
As the clock ticked into injury time, Norshahrul had one final chance to grab a consolation when he raced towards goal and let fly with a shot that looked destined for the far corner despite Izwan getting a glove on it.
Unfortunately for the hosts, the ball came back off the post and landed into the grateful arms of the Singapore goalkeeper, capping off a wonderful night at the office for Singapore.
Malaysia: Khairul Fahmi, Bunyamin Umar (Mahalli Jasuli 60'), Aidil Zafuan, Fadhli Shas, Azmi Muslim, Khyril Muhymeen Zambri (Wan Zack Haikal 46'), Amar Rohidan (Azamuddin Akil 78'), Safiq Rahim, S. Kunanlan, Norshahrul Idlan Talaha, Safee Sali.
Singapore: Izwan Mahbud, Daniel Bennett, Baihakki Khaizan, Safuwan Baharudin, Shaiful Esah (Irwan Shah 69'), Shi Jiayi (Fazrul Nawaz 90'), Mustafic Fahrudin, Hariss Harun, Shahdan Sulaiman, Shahril Ishak (Aleksandar Duric 73'), Khairul Amri.
ESPN STAR Sports will broadcast all 18 matches with the most extensive online coverage on the AFF Suzuki Cup. Check espnstar.com (espnstar.my or espnstar.co.id) for local TV listing & breaking news. Follow us on Twitter @espn_star (or @espnstarmy, @espnstarid) for the latest updates from Kuala Lumpur and Bangkok.