By Gabriel Tan at the Jalan Besar Stadium
The 28-year-old opened the scoring for the hosts five minutes after the half-hour mark when he clinically fired into the top corner, before grabbing a vital second in the 80th minute when he nodded home an inch-perfect delivery from Safirul Sulaiman.
The result meant the LIONSXII's hopes of winning silverware in their debut season in Malaysian football is still alive, although a tough test awaits them in the semi-finals when they take on high-flying ATM, who saw off defending champions Negri Sembilan 6-3 on aggregate.
Despite impressing many with their performances in the Malaysia Super League earlier this year, where they finished as runners-up behind Kelantan, the LIONSXII have been underwhelming in the Malaysia Cup so far and only narrowly progressed from Group A.
Having scored just five goals in seven games in the competition prior to Tuesday's encounter, many doubted if V. Sundramoorthy's charges would have what it takes to see off an attacking Pahang outfit, who won promotion from the Premier League just months ago.
Just two minutes in, the visitors almost opened the scoring when Malaysia international Azamuddin Akil latched onto a neat through-pass from Maycon Carvalho and played a dangerous ball across the face of goal, only to see Baihakki Khaizan deny Fauzi Roslan an easy tap-in with a vital clearance at the far post.
Azamuddin once again found space inside the area in the seventh minute when he surged past Irwan Shah after Baihakki had gave possession away in a dangerous area, but could only fire wide after slipping his shot through the legs of the onrushing Izwan Mahbud.
Two minutes later, he was at it once again as he neatly slipped Fauzi through down the left but this time, Izwan was equal to the task and made a smart save down low to keep the scores level.
Nonetheless, the hosts gradually settled and created their first real opening in the 13th minute when a searching diagonal ball by Hariss Harun was chested by Shahril into the path of Khairul Amri, who sent a half-volley on the turn narrowly wide of the top corner.
Two minutes after the half-hour mark, the LIONSXII's prowess at set-pieces nearly served them well when Baihakki leapt highest inside the opposition area and met a Shaiful Esah throw-in with a header that was just off target.
But three minutes later, the pressure eventually paid off when a loose ball on the edge of the area was hooked back into the danger zone by Hariss, where Shahril proceeded to plant a header past Wan Azraei's despairing dive.
With the aggregate score now 2-2 and with an away goal to their advantage, the LIONSXII started to play more conservatively after the break but it nearly cost them in the 52nd minute when Russian playmaker Boris Kochkin beat two men down the right and was presented with a clear sight at goal, only to drag his left-footed effort wide.
Right on the hour mark, the LIONSXII had a glorious opportunity to double their lead when Agu Casmir, who came on towards the end of the first half for the injured Amri, dispossessed Saifulnizam Miswan on the edge of the area before slipping Hariss through. However, with only Wan Azraei to beat, the 21-year-old blazed over from 12 yards out.
Two minutes later, Casmir himself had an even-better chance after Hariss, eager to make amends for his earlier miss, charged down the right and cut the ball back to Shahril. Despite having the whole goal to aim for, the LIONSXII skipper unselfishly laid the ball left to his fellow Singapore international, only to see him inexplicably poke a shot wide from six yards out.
While the attacking intent showed by the hosts was being appreciated by the home fans, it was starting to leave a number of gaps for Tok Gajah to exploit and Hafiz Kamal did well in the 68th minute to create space for himself, before unleashing a 35-yard strike that had Izwan scrambling to his far post to make the save.
Two minutes later, Casmir was guilty of wastefulness once again when he failed to hook the ball towards goal from close range, after Safuwan Baharudin had met a freekick by Shahdan Sulaiman and played the ball back across the six-yard box.
It was beginning to look like one of those days where the LIONSXII's profligacy might just come back to haunt them, but ten minutes from time, Shahril gave them the insurance they needed when he scored with another header, this time after Safirul had broken down the left and floated an excellent cross straight onto his head.
Now leading 3-2 on aggregate, the LIONSXII wisely sat back and retained possession and unlike a few weeks ago when they deliberately played for a 0-0 in their final Group A game against Johor FC, the home fans were cheering with every pass that was completed.
Two minutes from time, they could even have added a third when Casmir found space down the left and played a neat ball back to the edge of the area to Hariss, who sent a rasping 25-yard drive just wide.
Still, they had done enough by then to book their place in the last four of the competition and perhaps more importantly, win back the hearts of the Jalan Besar Stadium faithful.
LIONSXII: Izwan Mahbud, Irwan Shah, Safuwan Baharudin, Baihakki Khaizan, Shaiful Esah, Isa Halim, Hariss Harun, Shahdan Sulaiman, Shahril Ishak (Firdaus Kasman 90'), Safirul Sulaiman, Khairul Amri (Agu Casmir 37').
Pahang: Wan Azraei Wan Teh, Jalaluddin Jaafar, Zaiza Zainal Abidin (Faizol Hussain 86'), Saifulnizam Miswan, Shahrizal Salleh, Azamuddin Akil (R. Surendren 63'), Hafiz Kamal, Boris Kochkin, R. Gopinathan, Fauzi Roslan, Maycon Carvalho.