It is now impossible for the Knights, who sat 14th on the ladder after 19 rounds, to be ousted from the top eight with a week to play in the regular season.
Ponga guided the Knights to Sunday's home victory, scoring their first try, putting them in position for their second and setting their fourth up as the Knights scored five unanswered four-pointers after halftime.
But the Newcastle captain lay in pain on the ground after receiving a late hit from Sharks centre Jesse Ramien ahead of Newcastle's fourth try in the final 20 minutes.
Ponga surrendered goalkicking duties to Dane Gagai but tried to play through the discomfort.
When Greg Marzhew crossed and put the result beyond doubt in the final 15 minutes, Ponga came off with what was believed to be an injury to his acromioclavicular (AC) joint.
Knights coach Adam O'Brien had no prognosis post-match, but with a home final now locked up intimated he could rest Ponga for the clash with St George Illawarra next week even if the injury wasn't serious.
Dane Gagai or Lachie Miller appear the likely options to come in.
"I won't be stupid with (Ponga) that's for sure," O'Brien said.
"Lachie Miller hasn't left us yet. He's training well.
"He'll come in and do a good job."
Any long-term absence would be disastrous for Newcastle, given Ponga's pivotal role in resurrecting their season.
The Knights are already missing the other key cog in their attack, halfback Jackson Hastings, whose ankle injury forced him out of a second consecutive game on Sunday.
Despite the gaping defeat, the Sharks have likely done enough to seal a finals berth of their own.
They would only miss out if they lost by a large margin to Canberra next week, South Sydney beat the Sydney Roosters and North Queensland thrashed reigning premiers Penrith.
"It was disappointing in the end, that second half. We were just defending our tryline the whole day," Sharks coach Craig Fitzgibbon said of the Knights loss.
"I didn't think we exerted any pressure on them, we just kept releasing it."
The lowest Newcastle can finish is sixth, meaning they will host a home final for the first time since 2006 even if they lose to 16th-placed St George Illawarra next week.
"We didn't speak about grand finals in the summer but we spoke about how good would it be to be in a semi-final at home," O'Brien said.
"I'm really proud of the boys to achieve a goal that we set a long time ago."
After his opposite man Connor Tracey opened the scoring, Ponga shrugged out of a Matt Moylan tackle to level the scores 6-6 at halftime.
Ponga helped the Knights to their first lead of the afternoon when he beat five defenders and belted 50 metres on a kick return.
"That was a massive play," O'Brien said.
The Sharks' defence was still recalibrating when Bradman Best scythed through on the left for a try that confirmed all momentum for the Knights and they never looked back.
