Prior to Saturday's 22-10 loss, the three-time reigning premiers had lost only one of their last 80 games when leading at halftime by double digits, but were powerless to stop a Dragons side that ran in 22 unanswered second-half points.
Eight Origin representatives were missing across the two sides on top of injuries and a sloppy affair unfolded before 12,025 fans - the Panthers' smallest BlueBet Stadium crowd since the COVID-affected 2020 season.
It was another Jekyll-and-Hyde performance for the Dragons, who were error-prone, under pressure and incoherent with the ball in the first half.
But from the literal first moment of the second half, the script flipped dramatically.
In only his second NRL game and after a tough first half, right winger Sione Finau, sprinted through the Penrith defence from the kick-off for the second half and was only brought down on the halfway line.
The visitors never looked back.
With Ben Hunt on Origin duty, Jesse Marschke was called in for his first game as an NRL halfback and had a hand in the two tries that wiped Penrith's 10-0 halftime lead within 10 minutes of the restart.
He first changed direction with a short ball to Toby Couchman, who spun over on return to the first-grade side, and then sent a grubber kick through line for fullback Tyrell Sloan.
Tyrell Sloan celebrates after scoring against the Panthers. (Mark Evans/AAP PHOTOS)
Mat Feagai and Raymond Faitala-Mariner, St George Illawarra's best forward on the right edge, confirmed the result with four-pointers of their own in the space of four minutes.
The Panthers missed a golden chance to finish a weekend atop the ladder for the first time this season, unable to string sets together after the break.
They missed Dylan Edwards, Brian To'o, Jarome Luai, Isaah Yeo and Liam Martin to Origin duty - and lost Moses Leota to a minor hamstring injury mid-game - but their major issues were with the fundamentals of the game.
Penrith completed only three sets across the first 20 minutes of the second half as the Dragons found themselves on top of the game, and had some uncharacteristic moments of madness.
Nathan Cleary's injury replacement Brad Schneider timed out on a dropout, conceding a penalty, before Izack Tago spilt the ball from a play-the-ball coming out of trouble.
Replacement five-eighth Jack Cole set up the Panthers' only two tries, but they were a distant memory once the Dragons got going.
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