By Gabriel TanFollow @@gabetan13
Although there is still one game remaining in the group stage, the Red Giants can no longer finish inside the top two and qualify for the quarter-finals.
Entering Tuesday's game needing a win to keep alive their hopes of progress, it was never going to be an easy task coming up against ATM and it was the hosts who took the lead eight minutes before the break when Marlon Alex James scored.
The visitors did manage to equalise in the 73rd minute through a rare strike from Fitri Shazwan but they were unable to find a second goal, and will now have to wait another year to complete their much-publicised "Mission 33".
To make matters worse for Selangor, their local rivals PKNS FC became the first team to book their place in the last eight after cruising to a crushing 5-0 win over T-Team in Group B.
Roman Chmelo opened the scoring at the Shah Alam Stadium in the 20th minute, before a quickfire double by Patrick Ronaldinho Wleh saw the hosts claim a three-goal lead inside the opening half hour.
Chmelo then grabbed his second of the night in the 65th minute, before Nizad Ayub added a fifth for PKNS three minutes from time to cap off a fine performance.
Darul Takzim are in pole position to join PKNS in the quarter-finals after moving three points clear in second place with a 5-2 victory over FELDA United at the Temerloh Mini Stadium, which also ended the hosts' hopes in the process.
After Norshahrul Idlan Talaha had given Harimau Selatan a 15th-minute lead, Nurul Azwan Roya made it 2-0 in the 59th minute before Safiq Rahim added a third from the penalty spot two minutes later.
FELDA did manage to pull one back in the 73rd minute through a strike from Rudie Ramli, but 19-year-old forward Hadin Azman restored the visitors' three-goal advantage just three minutes later.
As the clock ticked over into injury-time, Rudie struck again to grab another consolation for the hosts but the night belonged to Darul Takzim, who completed the rout shortly after when Azwan Roya grabbed his second and his side's fifth.
In the other Group A game, Johor threw away a two-goal lead and had to settle for a 2-2 home draw against Sime Darby, meaning both sides are still in the running to make the quarter-finals.
Farid Ideris fired the hosts ahead in the 14th minute and when Izuan Jarudin doubled their tally seven minutes after the half-hour mark, it looked as though they were cruising to victory.
But three minutes before halftime, Azmirul Azmi pulled one back for Sime Darby and they struck again in the 57th minue when Fazrul Hazli equalised to earn them a share of the spoils.
Defending champions Kelantan edged closer to the knockout round after beating East Coast rivals Terengganu 3-1 at the Sultan Ismail Nasiruddin Shah Stadium.
An own-goal by Hasmizan Kamarodin handed the Red Warriors the lead in the 27th minute, and they edged further ahead three minutes before the hour mark when ex-Malaysia international Indra Putra Mahayuddin found the back of the net.
The hosts did manage to pull one back in the 74th minue through an Ashaari Shamsuddin effort, but any hopes of a late comeback were extinguished five minutes from time when Badhri Radzi netted Kelantan's third to wrap up the points and eliminate their opponents.
Kelantan remain second in Group C behind Pahang on goal difference, after Tok Gajah cruised to a 3-0 victory over Negeri Sembilan.
Following a goalless first half at the Darulmakmur Stadium, the deadlock was broken six minutes after the break when Matias Conti struck, before R. Gopinathan found the back of the net to make it 2-0 in the 70th minute.
Six minutes from time, midfielder Azidan Sairudin curled home a lovely freekick in off the post to seal the win for Pahang.
Finally in Group D, Kedah grabbed their first win of the campaign by beating Perak 1-0 thanks to Nelson San Martin's injury-time winner.
Tuesday's Malaysia Cup Results
ATM 1-1 Selangor
Johor 2-2 Sime Darby
FELDA United 2-5 Darul Takzim
PKNS FC 5-0 T-Team
Pahang 3-0 Negeri Sembilan
Terengganu 1-3 Kelantan
Perak 0-1 Kedah