By Gabriel Tan at the Jalan Besar Stadium
Loyola went behind in the 43rd minute when Eagles star Michael King tapped home after a goalmouth scramble, but they hit back two minutes after the hour-mark when Mark Hartmann scored with a fantastic half-volley from the edge of the area.
With neither side able to find another goal in the remaining half-hour, the game then went into extra-time, where the Sparks went on to claim the victory in the 95th minute through centre-back Park Min-ho.
In doing so, they also became the first foreign side to win in the competition this season, after Phnom Penh Crown and DPMM FC bowed out earlier in the week, and assistant coach Vincent Santos believes they were deserving victors.
"I wouldn't say we were lucky to win," Santos said when asked if he felt his side had been a little fortunate. "I think we deserved it.
"We had chances in the first half that we let by, luckily in the second half we were able to convert, but I wouldn't say it was a lucky win.
"Our back four held up pretty well, Mark Hartmann, who was playing in central midfield for the first time, distributed the ball really well today [Friday]. James and Phil [the Younghusband brothers] were useful as our go-to players, but I think it was a real team effort."
In an opening period that was largely dominated by Geylang, it was the Sparks who created the first chance in the fourth minute when Phil Younghusband met a delivery from Hartmann and headed just wide, before he fired a shot too close to Yazid Yassin eight minutes later, after his older brother James had capitalised on some poor defending by Rhema Obed and slid him in.
With the foreign team displaying their intent right from the start, Geylang began to up their tempo and were unlucky not to go ahead in the 26th minute, when King 's fiercely-hit 25-yard freekick took a nick off the wall and had Ref Cuaresma beaten all ends up, only to come back off the post.
Four minutes before the break, Yazid, as he has many times this season, came to the Eagles' rescue when he dived low to beat away a rasping drive from Hartmann, and his save proved vital two minutes later when his side went ahead.
The Loyola defence failed to deal with a long ball from Rhema Obed, allowing it to bounce all the way through to Rizawan Abdullah. Cuaresma did well to rush out bravely and deny the 24-year-old at his feet but fortunately for Geylang, the ball dropped straight to King who made no mistake from ten yards out.
It would have been easy for Loyola's spirits to have been deflated after conceding so close to the break but instead, they came out for the second half looking rejuvenated and came close in the 58th minute when James Younghusband drilled a shot across the fact of goal that was almost turned in by Jake Morallo at the far post.
Nonetheless, the Filipino side got the goal their endeavour deserved two minutes later when the older Younghusband broke down the right and whipped in a brilliant cross straight to Hartmann, who controlled the ball sublimely on his chest before firing a half-volley into the bottom corner.
However, fatigue soon set in on Loyola and they spent the remainder of the game playing with ten men on several occasions, after a number of players started to collapse with cramp.
Still, their backline held firm all the way to the end to force extra-time, and five minutes in, they hit the front when Park latched onto a loose ball on the edge of the area and fired a shot that came off Ishak Zainol's head and looped over a hapless Yazid.
With an opening-round exit staring them in the face, Geylang began to push more and more men forward and came close to levelling in the 119th minute when Syed Fadhil nodded a cross narrowly wide.
And right at the end, the Eagles had one final chance to bring the game to penalties when Mun Seung-man broke free inside the box and rounded Cuaresma. But from a tight angle, the South Korean decided to go for goal instead of squaring the ball to a waiting King, and ended up firing his side's final chance into the sidenetting.
While he was quick to stress he was pleased with all his players on the night, Geylang coach V. Kanan did admit that two personal errors ultimately cost them the win.
"I'm very proud of my boys," he said after the game. "They played hard for the whole 120 minutes.
"I think we were the better team - we created more chances, especially in the first half.
"[For the Loyola equaliser], our left-back Ang Zhiwei was ou so Mubarak [Ahmad] had to cover for him down the left. From there, the ball was played in behind him and they scored from that. That was the turning point of the game.
"Then, we had a chance right at the end that we should have scored from. Especially with Michael King waiting unmarked in the box, it was selfish of Mun to have gone on his own because the angle was very acute. If he had just squared the ball, I think we would have gotten the equaliser and in a penalty shootout, that would have been just down to luck."
Loyola will now face the winner of Saturday's clash between Woodlands Wellington and Kanbawza FC in the quarterfinals.
Loyola Meralco Sparks: Ref Cuaresma, Alexandro Elnar, Park Min-ho, Jeong Byeong-yeol, Roxy Dorlas (Patrick Ozaeta 75'), Jake Morallo (Amani Aguinaldo 80'), Andres Gonzales, Mark Hartmann, Simon Greatwich (Davide Cortina 62'), James Younghusband, Phil Younghusband.
Geylang United: Yazid Yassin, Ishak Zainol (Khairulnizam Jumahat 106'), Syed Fadhil, Rhema Obed, Ang Zhiwei (Shah Hirul 62'), Michael King, Mubarak Ahmad, Mun Seung-man, Jalal, Jozef Kaplan, Rizawan Abdullah (Amy Recha 73').
Image courtesy of Mark Dilamanta (UFL Philippines, InterAKTV)