The Sharks appeared to have stolen victory in the dying minutes themselves when bench forward Tyson Frizell crossed to give the home side a 20-16 lead.
But when a short kick-off found touch - and a scrum was controversially awarded to the Panthers - one last chance was afforded the visitors.
That was all Michael Jennings needed, dancing through defenders to level the scores with just 34 seconds on the clock.
Panthers halfback Luke Walsh had a conversion attempt close to the sideline to seal the win, but his kick hooked in the wind and slipped past the left upright.
He didn't wait long for redemption, calmly potting a field goal from 20 metres out in the second minute of extra time to seal the win as the crowd of 7,848 let their feelings of disgust known to match officials.
Despite the dramatic finish, it was a dour contest for the most part as both sides struggled with troops missing.
A week after being blasted 36-4 on their home turf in a performance coach Shane Flanagan said lacked attitude, Cronulla took the field with even more reasons to fold.
They were missing their attacking fulcrum, Todd Carney, their inspirational skipper, Paul Gallen, and another half a dozen first graders to injury.
Penrith weren't short of missing troops themselves, with former skipper Luke Lewis (neck) missing out on a match-up against his future teammates and Travis Burns suspended, but they did welcome back another player headed to the Shire, Michael Gordon, playing his first match since breaking his leg in round one.
And it was Gordon who sparked the dour contest into action midway through the first half with a 40-metre bust which gave Walsh the room to set up the first of Coote's two tries with a clever grubber.
Cronulla had a player score a brace themselves, with rookie centre Ricky Leutele crossing twice, but it was not enough.