Penrith fullback Dallin Watene-Zelezniak was left to rue a costly penalty that invited Cronulla into a contest they looked to be well and truly out of at PointsBet Stadium on Thursday night.
The Panthers were in control of the game after skipping to a 14-0 lead but a brain snap by Watene-Zelezniak, who resented a tackle from Sharks halfback Chad Townsend and retaliated, saw the visitors penalised against the run of play.
Cronulla scored their first try shortly after through young gun Bronson Xerri and ran in a further three in the final 15 minutes to escape with a stunning 24-20 win.
"That brain snap I had let the team down and it won't happen again," Watene-Zelezniak told reporters after the game.
"Any penalty is a turning point but that was a big one because we had the ball. Looking back I regret it a lot. It was a brain snap and I'll work on that and make sure it doesn't happen again.
"Just the way he (Townsend) was talking and the late shot, I reacted to it poorly. I've got to learn how to control it in other ways and not make that mistake again."
Watene-Zelezniak said his coach Ivan Cleary was quick to address him after the game, while describing it as a moment of madness.
"Personally I think there's a lot of things in our control we need to improve at," Cleary said.
"We're learning tough lessons but they're the only ones you really learn. We're trying to embark on some change and hopefully the message is sinking in."
The Panthers hung tough despite being on the end of a 7-2 penalty count and being forced to make a 69 more tackles than the Sharks.
Cronulla were also dominant in field position late with 1750 running metres compared to the Panthers' 1278 on the back of 59 percent of possession.
"We did lots of things right tonight and had a lot of players put in pretty good performances," Cleary said.
"But there's a couple here or there letting us down. We just couldn't put it together for 80 minutes."
The loss was further compounded by a hamstring injury to Dean Whare, who left the field in the 50th minute.
Initial fears of a grade two hamstring strain couldn't be confirmed by the Panthers on Thursday evening with the Kiwi international set for scans to determine the severity on Friday.