Ponga on Wednesday night became just the seventh player sent off in 45 years of Origin, for collecting NSW rookie Tolu Koula high with 22 minutes to go in Sydney.
With Queensland leading 20-6 at the time, they surrendered the lead as the Blues claimed the biggest comeback in Origin history to take a 22-20 victory.
Ponga protested his innocence, but was told by referee Ashley Klein that it was a "shoulder charge" with "direct contact to the head".
In the Nine Network's commentary, NSW legend Andrew Johns said "there was no way it's a send off", while Maroons great Cameron Smith also protested the call.
But when pressed by media afterwards, Queensland coach Slater refused to bite.
"We can argue all we want, I haven't got any problems with it," Slater said.
"(Kalyn)'s OK, he feels he's let his team down. They happen at the back. I played that position, I know how it is.Â
"Spur of the moment, it was wet out there. Those things happen. I thought it was a courageous effort (from the team). I'm heartbroken for them."
Maroons captain Cameron Munster indicated he felt Ponga was unlucky.
"I thought it might have been head on head with the split on KP's ear, but the referee and bunker saw it differently," Munster said.
"It is what it is."
Never in Origin history has a call had such a significant impact on a match.
Five of the previous send-offs have come late in the game, having little bearing on the result.
The last man sent off, Joseph Aukuso-Suaalii, was given his marching orders in the eighth minute of the 2024 series opener, prompting a heavy Blues defeat.
But this was an even bigger call.
After Koula broke into space down the left edge, Ponga rushed across in cover and collected the Manly flyer as he was being brought down by Sam Walker.
Klein conferred with bunker official Chris Butler, telling him he believed it should be a send off before ending Ponga's night.
NSW then sprung to life, scoring three times in the final 18 minutes to take a famous victory at Accor Stadium.
Ponga had been one of the Maroons' best as they shot out to a 20-0 lead after 21 minutes, looking threatening from the opening touches.
If Ponga was to cop a grade-three shoulder-charge sanction, he would be ruled out of Origin II in Melbourne on June 17.
A grade-two charge or lower would free him to play in that contest.
Koula, meanwhile, won't play again until game two with both of Manly's next two matches coming in the next eight days.
PLAYERS SENT OFF IN AN ORIGIN GAME:
* Craig Greenhill (QLD) - High Tackle - 62nd minute, Game II, 1996
* Gorden Tallis (QLD) - Referee Abuse, 71st minute, Game I, 2000
* Trent Waterhouse (NSW) - Striking, 78th minute, Game III, 2009
* Jarome Luai (NSW) - Headbutt, 79th minute, Game II, 2023
* Reece Walsh (QLD) - Headbutt, 79th minute, Game II, 2023
* Joseph Suaalii (NSW) - High Tackle - 8th minute, Game I, 2024
* Kalyn Ponga (QLD) - Shoulder Charge - 58th minute, Game I, 2026.
