Co-captain Nathan Cleary was at his creative best as the Panthers ran out to an 18-0 lead after 15 minutes on Saturday and went to the break up 30-4.
For the second time in as many games, a key Eels player was injured in a hip-drop tackle with hooker Mitch Kenny crunching Iongi just after halftime at CommBank Stadium.
"Izzy is a suspected syndesmosis so someone else gets an opportunity," said Eels coach Jason Ryles.
Iongi hobbled off in significant pain, six days after J'Maine Hopgood ruptured his anterior cruciate ligament in a hip-drop tackle against St George Illawarra.
"The players don't mean to do it, but unfortunately it happens in the game," said Ryles.
Panthers hooker Kenny went to the sin bin for his shot on Iongi and is likely to face scrutiny from the match review committee.
But Ivan Cleary leapt to Kenny's defence at full-time.
"I don't think the hip-drop origin looked like that. It was a one-man tackle against a very fast, powerful player. At the time I actually thought, 'what a great tackle'," the Panthers coach said.
"I just find it unfortunate. When the hip-drop (term) was first introduced, it was totally different to that.
"It ultimately just feels like it's going back to 'if there's a body, someone killed him'."
Kenny's sin-binning was the only major sour note for an undefeated Panthers team that appears streets ahead of its NRL rivals this season.
Even the Eels, once considered the premiership heavyweights' bogey side, could not manage a red-zone tackle until they were down 18-0.
"There was obviously some great footy. I thought our defence set us up to have some good field position and we did some good things with that," coach Cleary said.
Parramatta managed to stem the bleeding after the break, and Ryles was pleased the ledger at least stood at three tries apiece for the second half.
Bench forward Matt Doorey joined Iongi on the sidelines later in the second half and the Eels fear he may have an ACL injury of his own.
Cleary had his best game of the season yet, helping a pair of former Eels to tries on the way to Penrith's early three-score lead.
He sent in-form second-rower Isaiah Papali'i over with a short ball and then rejoiced as Blaize Talagi reefed his kick out of Iongi's hands and went over.
Even Cleary's blunders turned to gold.
The halfback looked sheepishly at his teammates after his heavy left-foot kick ricocheted off the goalpost padding and sat up for Lindsay Smith to score.
"It was a fluke. As it came off my boot I thought it was dead on the full," Cleary admitted.
A grubber kick for Paul Alamoti made it four try assists and reignited the Panthers following a slower start to the second half.
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