By Gabriel Tan at the Jalan Besar Stadium
Fazrul Nawaz scored the only goal of the game six minutes before the half-hour mark when he reacted quickest to a Baihakki Khaizan flick-on and nodded the ball home, handing his side a valuable three points in the process.
The result, coupled with Wednesday's 1-0 win at ATM, means V. Sundramoorthy's men are now second on the table behind surprise leaders Pahang only on goals scored.
Furthermore, it was the first time both sides could be separated after they played out 1-1 draws on both previous meetings last season.
While it was the visitors who got off to the stronger start, it was the LIONSXII who carved out the first scoring chance after eight minutes when Shahril Ishak latched onto a searching ball by Faritz Hameed right and drilled in a low cross that Ramez Dayoub met with a scuffed clearance that could have gone anywhere. Fortunately for the Lebanon international, the ball looped straight up and dropped into the grateful arms of Norazlan Razali.
Two minutes later, Shahril once again broke free down the right and was able to pick out a team-mate with his cross on this occasion, but despite having plenty of time and space, Fazrul was only able to fire his effort from the edge of the box straight at the goalkeeper.
It was then Izwan Mahbud's turn to be called into action at the other end in the 14th minute when he had to push over a rasping drive from Amri Yahyah, who decided to go straight for goal after Selangor had been awarded a freekick 35 yards out.
The LIONSXII then had an excellent chance to open the scoring a minute later when Irwan Shah raced into space down the left and whipped a low ball into the box. Although the cross was just behind behind Shahril, it made its way to the unmarked Nazrul Nazari at the back post but his first touch was just too heavy, allowing Raimi Nor enough time to boot away the danger.
By now the hosts were looking extremely dangerous down the flanks and had another opportunity in the 23rd minute when Shahril's right-wing cross eluded both Fazrul and Norazlan and fell to Irwan, who looked odds on to score with the whole goal to aim for, only to be denied by a remarkable recovering save from the Red Giants custodian.
However, there was little Norazlan could do a minute later to prevent LIONSXII from taking the lead from the resultant corner. Leaping highest inside the area, Baihakki met Hafiz Abu Sujad's delivery and helped the ball goalwards, where Fazrul then proceeded to steal in ahead of the onrushing goalkeeper and nod the ball into the back of the net.
Six minutes after the half-hour mark, the visitors came close to equalising when Francis Forkey Doe expertly brought down a long ball on his chest and fired in a snapshot on the turn, but Faritz Hameed was perfectly positioned to save his side with a block just before the line.
Buoyed by that narrow miss, Selangor came out after the break looking galvanised and again enjoyed the dominant share of possession.
But just like it had been in the first half, the LIONSXII continued to look the more dangerous of the two teams and could have doubled their lead in the 63rd minute when Irwan raced through on goal after a defence-splitting pass from Isa Halim, only to fire straight at Norazlan, who did well to race off his line and make himself big.
Five minutes later, Doe, who was looking the likeliest source of a Selangor goal, found space inside the area and looked to bend an effort into the corner, but Izwan was equal to the task and clawed away his effort just as it was about to dip under the crossbar.
Nonetheless, with the visitors pushing more and more men forward, the LIONSXII threatened to grab a second and Safuwan twice came close doing just that shortly after the 70th minute
First, he just failed to keep his header on target after Norazlan had flapped at a Hafiz corner, before unleashing a blistering 35-yard freekick that crept narrowly wide of the post.
But for all their possession, the Red Giants looked bereft of ideas up forward and even the introduction of midfield general K. Gurusamy did little to change that, as the LIONSXII continued to comfortably repel whatever attacks their opponents could muster.
11 minutes from time, Selangor had one final chance to grab an equaliser when Doe created space for himself with a clever turn but drilled a low strike just wide of the bottom corner, as the LIONSXII held on to maintain their 100% start to the campaign.
LIONSXII: Izwan Mahbud, Faritz Hameed, Baihakki Khaizan, Safuwan Baharudin, Shakir Hamzah, Nazrul Nazari (Safirul Sulaiman 46'), Isa Halim, Hafiz Abu Sujad, Irwan Shah, Shahril Ishak (Izzdin Shafiq 90'), Fazrul Nawaz (Shahfiq Ghani 77').
Selangor: Norazlan Razali, Mahalli Jasuli, Ramez Dayoub, Asraruddin Putra Omar, Raimi Nor, S. Veenod (Fairul Aziz 80'), Bunyamin Umar, Abdul Shukor Jusoh (K. Gurusamy 65'), S. Kunanlan, Amri Yahyah (Ramzul Zahini 65'), Francis Forkey Doe.