THEY might not have a lot left to play for this season, but the Cronulla Sharks caused their third NRL upset in five weeks on Saturday when defeating Penrith 18-16 in thriller at Carrington Park.

Led by a barnstorming Andrew Fifita, the Sharks ran in four tries to three in a contest where the quality belied the muddy and slippery conditions from start to finish.

The result remained up in the air until literally the final second, with Panthers mounting one final attacking raid to try and pinch victory and maintain touch with the top of the NRL ladder.

The Sharks were resolute though and eventually snuffed out Penrith's last-ditch effort, adding another impressive win to their two recent fightback victories against the Broncos and Roosters.

"They really played with effort and commitment to each other," Cronulla coach James Shepherd said.

"The conditions made it difficult in the second half and it got into a grind there. It went set for set for a while.

"I wasn't worried that we would drop off, sometimes when things go against us we can fall away, but that's not typical of this group."

Fifita was the obvious difference between the two sides as he routinely off-loaded, beat the first defender or rattled bones with his 25 punishing tackles.

In all he covered almost 240 metres and set up the try which put the Sharks ahead.

Earlier, it was all Cronulla in the first 10 minutes of the match as repeat sets and penalties meant the Panthers did virtually nothing but tackle.

Their defence cracked in the ninth minute when Jeff Robson sent a perfect kick to the right edge where rising Sharks star Jacob Gagan flew high to take the ball and plant it spectacularly for the opening points of the match.

Michael Gordon converted from the sideline for a 6-0 lead.

With both sides laying some heavy tackles the 8,824 strong crowd began to enjoy themselves and in spite of the slippery surface, there was no shortage of ball movement.

In the 20th minute Panthers fullback Matt Moylan combined with Dean Whare to put Dallin Watene-Zelezniak over for Panthers, with Jamie Soward's wayward conversion attempt leaving things at 6-4 to the Sharks.

The Sharks hit back soon after thanks to another Robson kick. It was batted back by Wade Graham for Sosaia Feki to flick a smart pass to Gordon, who crossed but couldn't convert.

Alarm bells were beginning to ring for Panthers when Gordon made a break and was brought down by Moylan only for the ball to end up in Gagan's arms in the next play as he went in for his second.

Gordon missed the conversion, but at 14-4 all the momentum was with Cronulla.

However, Penrith didn't get into the top four by dumb luck and the impressive Moylan threw a perfect cut-out ball to Kevin Naiqama who scored in the left corner near half-time. Soward's radar was on the money this time as he made it 14-10 going into the break.

The early stages of the second half were a reverse of the first, with Penrith doing all the attacking and earning some repeat sets. This time it was Whare who capitalised, levelling scores with Panthers' third try after 50 minutes.

Soward put them in front with another tracer-bullet kick, but the defining moments were about to arrive.

The first of them came when Fifita made a big bust from his own half and showing more fitting of a half, he found fellow prop Sam Tagataese in support. He put his team back in the lead at 18-16.

Robson then took charge, gaining two line drop-outs in a row and pinning Penrith in their own end.

Finally the Panthers got a chance six minutes from full-time to attack. A break by Moylan had the Sharks defence in a panic before Gagan again stepped up to bundle Naiqama into touch.

A frantic final two minutes saw Penrith throwing the ball around with abandon to try and find a late try, but they couldn't manage it.

"Some of the urgency we showed in the last 15 minutes would have been a bit nicer earlier in the game," defeated coach Ivan Cleary said of his team.

"The results in the last two weeks show what a tight competition it is, we have seen it all year.

"We can't take anything away from the Sharks, their completion rate was very high. They threw caution to the wind a few times with the ball too, so defensively we had to do a lot of work."

CRONULLA SHARKS 18 (Jacob Gagan 2, Michael Gordon, Sam Tagataese tries; Michael Gordon goal) defeated PENRITH PANTHERS 16 (Dallin Watene-Zelezniak, Kevin Naiqama, Dean Whare tries; Jamie Soward 2 goals)