Best laid plans, like winning through week one of the NRL finals to earn a break, can be derailed by even the most minor dips in form.

After a season of injury disruptions, bulk State of Origin duty and a battle with dreaded second-year syndrome, the Panthers showed signs of vulnerability in their shock qualifying final loss to South Sydney last week.

It was just their sixth loss in two years, but it threw another spanner in the works of a season that has been anything but smooth.

Being a juggernaut on a winning streak means every week is a battle against a side that has prepared to the hilt to meet a big challenge.

It can be draining, but coach Ivan Cleary says he sees no signs of it within his spirited young team.

"They are young, maybe that's part of the reason why we don't see the fatigue," said Cleary ahead of Saturday's semi-final against Parramatta.

"They enjoy playing footy.

"The idea was preferred to not have to play this week, but it's a different path so we are playing.

"I think when you do lose it's natural to want to get out there and perform better and that's been the whole focus this week.

"The vibe is very good as usual this year."

The speakers may be blaring at training but there's a nervous edge about the Panthers going into a sudden-death final this week.

Cleary's meticulous premiership planning started immediately after last year's grand final loss to Melbourne, when he admitted maybe the young team just was not ready for a premiership yet.

They've since lost experienced heads James Tamou and Zane Tetevano from their grand final side, but gained another year of wisdom.

On the back of a 12-game winning streak to start the season seven players were picked to play State of Origin, including debutants Brian To'o, Jarome Luai and Liam Martin.

Then halfback Nathan Cleary was struck down with a shoulder injury that threatened to end his season, while To'o, Luai, star prop James Fisher-Harris, fullback Dylan Edwards and Apisai Koroisau have all missed games through the season.

Luai's form, too, has taken a dip since returning from Origin duty.

His selection for the Blues came in his second full season of NRL and on the back of unstoppable form for the Panthers.

However, a drop off in runs, running metres and try assists since returning to the Panthers in round 19 shows the 24-year-old is playing far below his dynamic best.

Compared to last season, 2021 has not been easy sailing.

Cleary had planned for fatigue and burnout at the end of the season, but given everything the year has thrown at them, they're adapting on the run.

"We do thorough planning, there's certainly been a different season for us, completely different circumstances but we feel like we're in a very good position right now," coach Cleary said.

"It's just a challenge, part of your planning is just contingencies, you can't plan for everything.

"But we welcomed the Origin contingent and having so many players there, we always felt like it was going to be a good thing but in the short term it's also a challenge.

"We've had our injuries as well but that's just how it is.

"It's just a different path, it's just a different opportunity, it's a different experience for us.

"It's a young team still on a journey and we've got a long path in front of us.

"But we're in great shape, we're feeling good.

"Last week was just a hiccup, really. We've just got to play better."

While the young Panthers are learning on the run, so are their NRL rivals.

As quickly as Penrith nail something down, their more experienced opponents are doing their homework just as fast - and therein lies the challenge for any team on top for as long.

Australian Associated Press