By Gabriel Tan at the Jalan Besar Stadium
Marlon Alex James opened the scoring in the 55th minute when he beat the opponents' offside trap and raced through to score, with what could yet prove to be a valuable away goal for the Armed Forces.
Nonetheless, Safuwan Baharudin ensured V.Sundramoorthy's side will head to Selayang with plenty to play for after he ventured forward nine minutes from time to send a thumping header into the back of the net.
Despite the confidence boost derived from Tuesday's 2-0 win over Pahang, which saw them overturn a one-goal aggregate deficit and progress from the quarter-finals, the LIONSXII started the game looking the more nervous of the two sides and nearly handed James an opportunity in the third minute when Shaiful Esah gave away possession to the 35-year-old inside his own half. Thankfully for the hosts, Baihakki Khaizan was on hand to deal with the threat with a well-timed challenge.
Eight minutes later, ATM had a good opportunity when Hairuddin Omar narrowly failed to connect with a long ball at the back post, before the LIONSXII fashioned a chance of their own in the 15th minute when Agu Casmir broke free down the left, only to send a cross inches behind Shahril Ishak.
Baihakki then came to his side's rescue again in the 21st minute when his perfectly-timed tackle halted the charge of James, who had looked set to charge down the left after an incisive pass from Azmi Muslim.
Given their strong start, it was beginning to look increasingly likely that the visitors would be the first to find the breakthrough but five minutes after the half-hour mark, the LIONSXII came close when Irwan Fadzli Idrus, under pressure from Casmir, misread the bounce of a clearance from Baihakki and sent the ball hurtling towards his own goal. Thankfully for the veteran, Farizal Harun reacted in time to save his team-mate's blushes.
Buoyed by nearly taking the lead, the hosts started to grow in confidence and ended the half the stronger of the two sides.
Shahdan Sulaiman had a decent effort parried away in the 39th minute when he let fly from 25 yards, before Farizal showed good hands to cleanly gather a strike from Shahril, who was looking to curl one into the far post two minutes later.
However, all the LIONSXII's good work before the break was undone ten minutes after the break, when a lapse in concentration at the back allowed James to slip in behind Baihakki and latch onto a hopeful punt by K. Reuben. Given his clinical nature, there appeared to be only one outcome and it proved to be so as he calmly slotted past Izwan Mahbud and into the bottom corner.
Having played a key part in his side taking the lead, Reuben then had to be alert to head away a dangerous freekick by Shahdan in the 62nd minute, especially with the dangerous Safuwan lurking unmarked at the back post.
James then had another chance to double his tally in the 73rd minute when he expertly controlled another long ball after muscling his way past Baihakki only to blaze over from a tight angle, and eight minutes later, that miss proved costly as the hosts equalised.
Irwan Fadzli looked to have denied the Singaporean outfit a good opening when he illegally halted the run of Shahril, who looked set to break down the right, but he proved to have merely delayed the inevitable as Shahdan swung in the resultant freekick, straight onto the head of Safuwan who planted a bullet header past a hapless Farizal.
The LIONSXII's equaliser proved to be the last meaningful action in what had been a very eventful game, and both sides will head into next week's second leg at the Majlis Perbandaran Selayang Stadium confident in their chances of progressing to the final.
LIONSXII: Izwan Mahbud, Irwan Shah, Safuwan Baharudin, Baihakki Khaizan, Shaiful Esah (Sevki Sha'ban 61'), Hariss Harun, Firdaus Kasman (Yasir Hanapi 74'), Shahdan Sulaiman, Shahril Ishak, Safirul Sulaiman, Agu Casmir (Sufian Anuar 78').
ATM: Farizal Harun, K. Reuben, Aidil Zafuan, Fitri Omar (Venice Elphi 90'), Irwan Fadzli Idrus, Rezal Zambery, Hairuddin Omar, D. Christie Jayaseelan, Bruno Martelotto, Azmi Muslim, Marlon Alex James (Amiridzwan Taj Tajuddin 74').